Paulin Research Group
NozzlePRO Program Manual
Paulin Research Group 11211 Richmond Avenue, Suite 109 Houston, Texas 77082
Tel: 281-920-9775 Fax: 281-920-9375 Email:
[email protected][email protected]
Table of Contents Chapter 1 – About Nozzle Pro Section 1 – Version Features Section 2 – When to use NozzlePRO Section 3 – Sample Problems Section 4 – Sample Problem Details Section 5 – How to Get Help Chapter 2 – Using NozzlePRO Section 1 – Getting Started Section 2 – Stress Types Section 3 – Options Data Form Section 4 – Using the 3D Viewer Section 5 – How NozzlePRO Starts the DirectX Viewer Section 6 - Errors – Aborted Runs – and DirectX Troubleshooting Section 7 – FE/PIPE, NozzlePRO, PVElite, and CodeCalc Chapter 3 – Interpreting and Using the Results Section 1 – Output Review for 3D Shell Models Section 2 – Stresses and Allowables Section 3 – Pressure Design Using 3D Shell Elements Section 4 – Stress Intensification Factors and Flexibilities Section 5 – Allowable Loads Section 6 – Discussion of Results (Recommended Ways to Use the Output) Chapter 4 – Saddle Supports and Pipe Shoes Section 1 – When to Use NozzlePRO Saddle / Pipe Shoes Section 2 – Saddle and Pipe Shoe Input Screens and Saddle Wizard Section 3 – Applications of the Saddle / Shoe Modeler Section 4 – Interpreting the Results Section 5 – Integral vs. Non-Integral Wear Plates Section 6 – Other Topics Chapter 5 – Advanced Models Section 1 – NozzlePRO FFS Section 2 – Piping Input Screens Section 3 – Axisymmetric 2D and Brick Models Section 4 – Skewed Structural Supports in NozzlePRO Chapter 6 – Special Topics Section 1 – WRC Comparisons Section 2 – Engineering Considerations Section 3 – Finite Element Philosophies, Element Types, Etc.
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Axisymmetric Horizontal Vessel Modeling with Saddles Axial Load Evaluation for Horizontal Vessels Gravity Multipliers for X, Y, & Z Directions for Modeling Vessel Loads Solution Data Report a. Stiffness matrix information including maximum row size, largest stiffness coefficients, and stiffness coefficient distribution. b. Total number of nodes, elements, and solution cases c. Summation of loads at boundary conditions for each load case. Allows for verification of weight and loads applied to model and helps check for unbalanced loads. Pipe Shoe Modeler Integral & Non-Integral Wear Plates for Saddles and Pipe Shoes Tapered Saddles and Pipe Shoes SYMFIX Boundary Conditions for Midspan Ovalizing in Horizontal Vessels Upgraded DirectX 3D Dynamic Displacement and Static Model Viewer Nozzles through Blind Flanges in Axisymmetric and Brick Models Double Bed Support Axisymmetric and Brick Models Axisymetric 2d and Brick Axisymetric Models Steady State and Transient Heat Transfer for Axisymetric 2d Elements Blind or Matching Flange End Conditions for Axisymetric 2d or Brick Models Radius’d Welds in Axisymetric 2d and Brick Models Overturning Moments on Skirts (Brick Models) DirectX 3d Dynamic Displacements Internal Ring Loads in Axisymetric 2d or Brick Models
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Help Buttons Throughout Discontinuity Stress Reporting Integral and non-Integral Repads for Axisymetric 2d or Brick Models Head Thickness Contours for Bricks and Axisymetric 2d models Support for DirectX 3d Rendering Updates a. Three-Dimensional views of the geometry, stress or displacement state can be rotated, panned, zoomed or clipped in real time and sent to clients for viewing on their own computer. (See Files discussion below.) b. Translucent or hidden-line wireframe views may be manipulated. c. An interactive thermometer may be used to view the exact stress at any point in the model. d. Rubber-band, Viewport, or polyline clipping. e. Cut to Clipboard f. High Stress Call Outs g. Model Cutaway by Value or By Percentage 24- Structural Attachments a. Ten different structural attachment cross sections can be loaded on head, cone or cylindrical geometries. b. Attachments may be with or without a pad. c. Moment loads are applied automatically over the structural end section. 25- Unstructured Meshing Options for Heads & Structural Attachments a. Difficult-to-mesh structured geometries are often easily meshed using unstructured methods. Unstructured meshing is available for head or structural attachment models.
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26- Elemental Smoothing a. Elemental smoothing produces more uniform element grids and perfect geometric shapes not dependant on cubic approximations. 27- Cylinder Boundary Condition Control a. Users may free either the top or bottom of the cylinder and observe the effect on the stress distribution in the geometry. 28- Added Control of Weld Sizes a. The user may specify the weld length along either the branch or header (parent) and may also specify the weld size at the edge of any reinforcing pad. 29- Access to FE/Pipe Input Data Screens a. The user may access the FE/Pipe input data screens to provide any additional model, mesh or loading control that is needed. 30- Control of Element Stress Averaging a. The user may deactivate stress averaging if desired. 31- Saddle Wizard a. A step-by-step interactive modeler that allows the user to easily design horizontal vessel for any loading conditions. The Saddle Wizard now allows for full horizontal vessel models with one saddle fixed and the other saddle sliding. Earthquake or ship motion acceleration loads, pressure, temperature, and more can be applied to the model. 32- New File Handling
33- Dynamic Units Switching a. When switching between English and SI units, the input values are now converted from one system to the next units system. 34- Load Translation Calculator a. Nozzle/PRO users no longer need to have their loads given at the end of the nozzle. Loads can now be specified at the centerline of the header, header/branch intersection, or the end of the branch. 35- Pull Down Menus and User Navigation 36- Improved Brick Meshes of Nozzles in Heads 37- Example Models Using NozzlePRO
3d Viewer Screen
Structural Attachment Options Unstructured Mesh
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Top Head Blind & Pad
Pipe Shoe
Size-on-Size Pad
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Bottom Head Skirt
Brick Flanges & Skirt
Triple-Plate Support
Hillside Nozzle Pad Reinforced Nozzle
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Top Head Load Flanges
Head Structural Support
Reinforced Lateral in Cone
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Pipe Shoe Options
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Horizontal Vessel with Saddle Support
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Chapter 1 – Section 2 When to Use NozzlePRO Typical occasions when a finite element analysis of a NozzlePRO geometry is beneficial are listed below: 1) When the d/D ratio for a loaded nozzle is greater than 0.5 and WRC 107/297 is considered for use. 2) When the t/T ratio for a loaded nozzle is less than 1.0 and WRC 107/297 is considered for use. 3) When the nozzle is pad reinforced and WRC 107/297 is considered for use. 4) When the number of full range pressure cycles is greater than 7000 cycles and the nozzle is subject to external loads. 5) When the D/T ratio is greater than 100 and SIFs or flexibilities are needed for a pipe stress program. 6) When the D/T ratio is greater than 100 and a dynamic analysis including the nozzle is to be performed using a piping program. 7) When a large lug is used in a heavily cyclic service. 8) When pad-reinforced lugs, clips, or other supports are placed on the knuckle radius of a dished head. WRC 107 simplifications for pad reinforced rectangular lug attachments are fraught with potentially gross errors. 9) When seismic horizontal loads on vessel clips or box supports are to be evaluated. 10) Pad reinforced hillside nozzles subject to pressure and external loads. 11) Large run moments, but small branch moments in a piping system. 12) Overturning Moments on Skirts 13) Effect of Integral vs. Non-Integral Pad on Nozzle in Head Should be Studied 14) Different thermal expansion coefficients or temperatures between the header and branch. 15) Where loads on nozzles are high because of the assumption that the nozzle connection at the vessel is a rigid anchor. Few connections at vessels are “rigid.” Often only small rotations can significantly reduce the calculated moment and stress. Accurate flexibilities permit the actual moment on the vessel nozzle to be calculated and designed for. 16) Heat Transfer in An Axisymetric Model Geometry 17) When the effect of adding a radius to weld geometries on nozzles in heads should be investigated. 18) To verify FEA calculations. NozzlePRO4 allows nozzles in heads to be analyzed with shell, axisymetric, or brick finite elements. The analyst can run each model type and compare results to determine the stability and accuracy of the solution. 19) For saddle supported horizontal vessels with or without wear plates including tapered saddles with many design options. 20) To evaluate effects of axial or transverse loads due to internal sloshing, wind loads, seismic loads, or general external loads. Zick’s methods do not consider axial or transverse loads. 21) Design of Pipe Shoes for self-weight, liquid weight, and external loads. Criticality of the application is a major consideration when deciding whether or not to run a finite element calculation. Hot hydrocarbon products are clearly more dangerous than ambient temperature water processes and should be approached with increased caution. Systems that do not cycle are less prone to failure than systems that cycle daily. Extreme design conditions can also make using less conservative, more accurate approaches practical. Large d/D, D/T intersections are difficult to analyze properly for a combination of pressure and external loads, and FEA results tend to give more consistent results over a broader range of problem parameters. Allowable loads on vessel nozzles give the piping engineer guidance when evaluating thermal loads on anchors. Higher earthquake load requirements can make conservative design assumptions costly. Caution should be excercised when low pressure-high temperature systems are evaluated as these lines tend to have high loads and large d/t ratios. “It is absurd to use FEA on every system, and it is absurd not to use it at all.” Copyright (c) 2007 by Paulin Research Group
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Chapter 1 – Section 3 Sample Problems Several examples illustrate. (Details for each example are included in a separate chapter at the end.) Example Problem Description Cylindrical Junction (WRC 107) NonLoaded Small Branch Takeoff Nozzle Loads Due To FEA Flexibilities SIF’s for Nozzles in Heads Straight vs. Lateral
Small d/D WRC 107 Comparison Pad Reinforced Attachment
Difference with FEA FEA Stress 270% Higher than WRC 107 FEA Stress 500% Lower than B31.3 FEA Loads 630% Lower than Rigid Analysis FEA Stress 7.7 Times Higher than Piping Program Default Lateral 1.34 Times Stronger Than Straight Nozzle InPlane Lateral 1.7 Times Stronger Than Straight Nozzle Outplane Lateral 2.2 Times Weaker Than Straight Nozzle for Pressure FEA different from WRC 107 by 3.7% FEA Stress 1.8-to-10.0 Times Higher than WRC 107
Process Feed Line: A process feed line to a vessel cycles about every 6 hours. In 20 years this is 29,200 cycles. The number of design cycles is greater than 7000, so the safety factor against failure is as low as it can get, (about 2.0 ref: Nureg/CR-3243 ORNL/Sub/82-22252/1). The engineer decided that a good stress calculation was important since the number of cycles was high. The d/D ratio was only 0.27, but the geometry was pad reinforced. WRC calculations were not intended for pad reinforced geometries, and this is reflected in the results when the FEA calculation is compared against WRC 107. WRC 107 Stress at Junction: WRC 107 Stress at Pad Edge: FEA Maximum Stress (PL+PB+Q out) with 1.75x mesh FEA Maximum Stress (PL+PB+Q out) with 1.75x mesh
21,490.psi. 18,214.psi. 65,887 psi. (307% of WRC 107) 69,688 psi. (324% of WRC 107)
Gas Riser: The 400F 18” riser was only subject to 10 psig of internal pressure. Thermal moments produced less than 10,000 psi of stress in the pipe except at an 8” takeoff that was valved and capped. The stress at this unloaded branch connection showed to be in excess of 55,000 psi. A finite element calculation of loads through the header showed that the actual stress was less than 9,000 psi. The line was not even close to being overstressed, there was no reason for redesign or rerouting of the pipe. B31 Piping Code: Nozzle/PRO:
Se = (io)(Mo)/Z = (6.1)(1.1E6)/(120.3) = 55,777 psi Se = (io)(Mo)/Z = (1.0)(1.1E6)/(120.3) = 9,143 psi
So the actual stress is 1/ 5th B31 Value Nozzle Loads: Using rigid anchor assumptions, the conservatively estimated loads on the vessel nozzle were in excess of 344,844 ft. lb. When flexibilities were inserted at the nozzle, the moments due to the piping loads dropped to 53,981 ft.lb., a
reduction of 153 times.
Allowable Loads and Pressure MAWP: The process engineer wanted to slope the process vent lines into the header to improve flow and reduce the potential backpressure buildup in the header. He didn’t want to create a much weaker junction, however by using a connection at 45 degrees. He wanted to know which of the connections was stronger for bending moments – the straight 90 degree intersection, the 45 lateral, or the hillside connection. The vent header was 24” x 0.375” wall, and the vent outlet was 16” x 0.375” wall. The results from NozzlePRO are shown below and confirm what is generally known about these intersections. The larger footprint of the lateral improves the moment carrying capacity, but cuts a larger hole in the header in the longitudinal direction increasing the hoop stress effect. The hillside in this d/D ratio performs essentially as well as the straight through intersection. Copyright (c) 2007 by Paulin Research Group
1.3.1
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InPlane Max Allowed Moment Outplane Max Allowed Moment Maximum Allowed Pressure
Straight Through
Lateral (45)
Hillside
B31.3
583,179 in.lb. 171,867 in.lb. 348 psi
786,243 in.lb. 304,402 in.lb. 160 psi
451,108 in.lb. 191,997 in.lb. 326 psi
495,658 in.lb.1 385,698 in.lb. n/a
Good Comparisons with WRC 107: The engineers were concerned that some of the results from the FEA calculation were different from WRC 107 programs. When calculations are run that keep the limits of the WRC 107 approach in mind, the comparisons are much better. Leaving out pressure effects, (which are not included in WRC 107), using a small d/D, only a single moment loading, and a t/T ratio greater than 1.0, the comparisons between FEA and WRC 107 are much better: Stress (psi) WRC 107 FEA tn=0.5” FEA tn=0.9” FEA tn=1.5”
126,677 150,765 144,522 131,579
Rectangular Attachments (WRC 107): As might be expected, WRC 107 for a rectangular attachment that has essentially the same dimensions in the longitudinal direction as the 8” pipe above produces essentially the same stress. The FEA model shows higher stresses around the corners of the geometry where the stress is concentrated. The FEA model also shows the beneficial effect of pads and the gross errors that can occur when WRC 107 is used for pad type attachment geometries. WRC 107 Pad Lug (1) (2) Edge Edge 141,818 n/a 43,215 90,929 43,215 34,639 43,215 22,619 43,215 22,619 43,215 22,619
Line Load(3) Lug Pad (1) (2) Edge Edge 111,139 n/a 39,462 67,989 39,462 24,909 39,462 15,619 158,145 15,619 299,006 15,619
6x8 Rectangle No Pad 6x8 Rectangle 1” Wide Pad 6x8 Rectangle 4” Wide Pad 6x8 Rectangle 6” Wide Pad 6x8 Tri Plate Supt. 6” Wide Pad 6x8 Inverted Tee 6” Wide Pad Notes: (1) Simulated by increasing vessel thickness. (2) Simulated by increasing Load Bearing Area. (3) Ref: H. Bednar, Pressure Vessel Design Handbook, Van Nostrand, New York, 1981.
Box (no Pad) (129,813)
Box (1” Pad) (71,197)
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FEA Lug (1) Edge 129,813 71,197 46,775 41,299 42,311 75,275
Pad (2) Edge n/a 70,604 30,960 24,257 24,358 24,631
Box (4” Pad) (46,775)
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Box (6” Pad) (41,299)
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Triple-Plate (42,311)
Inverted Tee(75,275)
Example 6 – Using FE/Pipe and Nozzle/PRO SIFs in Pipe Stress Programs: ASME B31 SIFs published in 1955 were determined experimentally using tees having the same branch diameter and thickness as the header diameter and thickness (d/D = 1 and t/T = 1). The ASME later (1965) introduced a correction factor for branch stresses when d/D < 1. The original SIF equations are still used by the codes: io = (0.9)[(tH)/(RmH)]2/3. > 1.0 ii = (0.675) [(tH)/(RmH)]2/3 + (0.25) > 1.0 FE/Pipe and Nozzle/PRO Stress intensification factors use the WRC 329 definition of “if”, or “ifailure”: These SIFs are based on the actual nozzle section modulus and do not require adjustment for branch connections smaller than the header.
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1.3.3
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Chapter 1 – Section 4 Sample Problem Details Example 1 - Process Feed Line (Pad Reinforced Nozzle) A process line to a vessel cycles about every 6 hours. In 20 years this is 29,200 cycles. The number of design cycles is greater than 7000, so the safety factor against failure is as low as it can get (about 2.0 ref: Nureg/CR3243 ORNL/Sub/82-22252/1). The engineer decided that a good stress calculation was important since the number of cycles was high. The d/D ratio was only 0.27, but the geometry was pad reinforced. WRC calculations were not intended for pad reinforced geometries, and this is reflected in the results when the FEA calculation is compared against WRC 107.
Geometry Vessel: 72” ID x 0.625” wall (73.25” OD) Nozzle: 20”OD x 0.5” with a 5” wide pad 0.625” thick
Loads Local MX = 3E6 in lb, Local MY = 2.79E5 in lb, Local MZ = 6E5 in lb
Model Geometry and coordinates are illustrated below. The blue axes show the Global coordinates (of the overall model), and the black coordinates show the Local Load coordinates (for the nozzle).
Building the Nozzle/PRO Model (Build and analyze in 6 steps) Step 1 of 6 Start Nozzle/PRO by double-clicking the desktop Short/Cut
Double clicking this icon should bring up the program screen below. If this screen does not appear or if the options are different than displayed, send an Email to [email protected] with a description of the problem.
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Step 2 of 6 Select Input Units (English or SI) For this example select “English” units
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Step 3 of 6 Select a “Base Shell Type” and input “Vessel” Dimensions For this example select “Cylinder” and input the vessel OD and wall thickness
Note these inputs are described in the images below
Step 4 of 6 Select a “Nozzle/Attachment Type” and input the dimensions For this example select “Pad” and input the Nozzle and Pad dimensions.
Note these inputs are described in the images below
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Step 5 o f 6 Input Loads Click the “Loads” button and the following screen should appear. Input the loads and use “locally” defined loads (convert to ft lb ) (Using local coordinates without direct shear loads permits the user to ignore nozzle length)
Local coordinates
Step 6 of 6 Run and Review Results This example only compares the calculated stresses of two methods. Since the objective does not include comparing stress to an allowable stress value, the allowable stress input is not used. Click “Run FE”. Once the analysis is complete, Nozzle/PRO will display a message indicating the run has finished. Click “OK”.
The Nozzle/PRO screen should appear as shown below. Output windows are described in detail in Chapter 3 Section 1, with additional instructions on how to use the 3d graphics window in Chapter 2 Section 3. For this example review plot “2) PL+PB+Q < 3Smavg (OPE outside) Case 1”
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Discussion of Results The finite element model and results plots are shown below:
WRC 107 Stress at Junction: WRC 107 Stress at Pad Edge: FEA Maximum Stress (PL+PB+Q out) with 1.75x mesh FEA Maximum Stress (PL+PB+Q out) with 1.75x mesh
21,490.psi. 18,214.psi. 65,887 psi. (307% of WRC 107) 69,688 psi. (324% of WRC 107)
FEA is 3.2 times higher than WRC 107 This is a typical problem when WRC 107 is used for a geometry it was not originally intended to address. Before the repad was added to the geometry, the t/T ratio was 0.5/0.625=0.8 < 1.0, and the high stress was in the vessel and WRC 107 would do a reasonable job of estimating the stress for this d/D ratio. With a 0.625” repad, the t/T ratio becomes: 0.625 / (0.5+0.625) = 0.555, and the high stresses move into the nozzle. Since WRC 107 does not calculate the stress in the nozzle, this high stress was completely missed. Over the years WRC 107 has been used for pad reinforced geometries since no other tools were available. Two analyses are typically made for pad reinforced nozzle geometries. One is for the edge of the repad. The nozzle OD is increased to equal the pad OD and the WRC 107 analysis run with the larger nozzle. For WRC 107 cylinder-to-cylinder intersections the thickness of the nozzle does not enter into the calculation. The second calculation is made with the actual nozzle Copyright (c) 2007 by Paulin Research Group
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OD and the increased local thickness of the vessel and pad. Parameter studies are under way to determine when this approach will produce the worst results, but large errors have been witnessed for certain geometries. This is not the fault of the WRC 107 bulletin. The bulletin has simply been extended beyond its intended range of usefulness by programmers needing to find solutions for problems in all parameter ranges.
Example 2 - Gas Riser The 400F 18” riser only saw 10 psig of internal pressure. Thermal moments produced less than 10,000 psi of stress in the pipe except at an 8” takeoff that was valved and capped. The stress at this unloaded branch connection showed to be in excess of 55,000 psi. A finite element calculation of loads through the header showed that the actual stress was closer to 9,000 psi. The line was not even close to being overstressed. There is no reason for redesign or rerouting of the pipe.
Geometry Riser Pipe: 18” OD x 0.5” wall Branch Pipe: 8.625 x 0.5” wall
Loads Pressure: 10 psig Thermal Expansion (outplane) Moment: Mo = 1.1E6 in lb. (450°F Furnace Gas)
Determine the “Header” SIF for the Overhead Line in 6 Steps Step 1 of 6 Start Nozzle/PRO by double-clicking the desktop Short/Cut Step 2 of 6 Select Input Units (English or SI) For this example select “English” units
Step 3 of 6 Select a “Base Shell Type” and input “Vessel” Dimensions In this example select “Cylinder” and input the vessel OD and wall thickness
Note these inputs are described in the images below
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Step 4 of 6 Select a “Nozzle/Attachment Type” and input the dimensions In this example select “Straight” and input the Nozzle dimensions.
Note these inputs are described in the images below
Step 5 of 6 Change the OPTIONS screen to calculate header or “header” SIFs This will set the basis of the calculation to be loads through the header rather than the branch. Click “OK” when finished to close the Options window.
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Step 6 of 6 Run and Review Results This example only computes stress intensification factors. Since the objective does not include comparing stress to an allowable stress value, the allowable stress input is not used. Click “Run FE”. Once the analysis is complete, Nozzle/PRO will display a message indicating the run has finished. Click “OK”.
The Nozzle/PRO screen should appear as shown below. Output windows are described in detail in Chapter 3 Section 1, with additional instructions on how to use the 3d graphics window in Chapter 2 Section 3. For this example review plot “2) PL+PB+Q < 3Smavg (OPE outside) Case 1”
A portion of the stress intensification factor report is shown below. The values to be used in a pipe stress analysis are the peak stress intensification factors. The primary and secondary SIF’s should be ignored for B31 applications, (there is no place is in the B31 Codes to use them.). Any SIFs calculated that are less than one should be increased to one before they are used. (See the torsional SIF below.) It is not unusual that a component is stronger than a girth weld in the attached pipe. (This is what the SIF is based on.) FEA results echo this result. If the component is big and thick, compared to the attached pipe, then the SIF could easily be less than 1.0. SIF’s less than 1.0 should never be used in a pipe stress analysis however. Always increase the value to 1.0 before using it. Stress Intensification Factors Branch/Nozzle Sif Summary
Axial : Inplane : Outplane: Torsion : Pressure:
Peak 1.991 1.846 0.503 3.146 0.000
Primary 2.004 1.801 0.974 4.539 0.000
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Secondary 2.949 2.735 1.007 4.660 0.000
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Compare with B31 Piping Code Stress Calculation Expansion Stress is calculated using the following equation Se = (io)(Mo)/Z
r2 = (0.5)(18 – 0.5) = 8.75 Z = (π)(r22)(T) = (π)(8.752)(0.5) = 120.3 io = 0.9/(T/r2)(2/3) = (0.9)/(0.5/8.75)(2/3) = 6.066 ~ 6.1
B31 Piping Code: Nozzle/PRO:
Se = (io)(Mo)/Z = (6.1)(1.1E6)/(120.3) = 55,777 psi Se = (io)(Mo)/Z = (1.0)(1.1E6)/(120.3) = 9,143 psi
So the actual stress is 1/ 5th B31 Value Discussion This problem is discussed in E.C. Rodabaugh’s WRC Bulletin 329. The results from the pipe stress analysis are shown below along with the FE/Pipe finite element result (Nozzle/PRO can not apply loads to the header).
The displaced shape of the piping model shows that the intersection is subject to outplane bending moments through the header (in fact the branch only supports the weight of the valve). The B31 piping codes do not make any differentiation between SIF’s for the header or branch at an intersection. Because of the overly-conservative assumptions in the piping code, a SIF of 6.1 is used by default at this intersection. The FEA analysis of the outplane moment shows that this SIF is actually be 1.0. (The nozzle on the side of the header does not sufficiently increase the stress above the maximum value at the outer fiber removed from the nozzle.) This is true for all nozzles with smaller d/D ratios. The stress for this problem as calculated incorrectly by the piping codes (see WRC 329) will be 6.1 times higher than it should be, and expensive rerouting or alternate supporting of the system might result unnecessarily. Appendix D of the B31 piping codes states that “Stress intensification and flexibility factor data ... are for use in the absence of more directly applicable data...” In this case, more directly applicable data (i.e., FEA analysis) and similar recommendations from WRC 329 could be used to avoid rerouting the piping system.
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1.4.9
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Example 3 – Allowable Loads and Pressure MAWP The process engineer wanted to slope the process vent lines into the header to improve flow and reduce the potential backpressure buildup in the header. He didn’t want to create a weaker junction however by using a connection at 45 degrees. He wanted to know which of the connections was stronger for bending moments – the straight 90 degree intersection, the 45 lateral, or the hillside connection. The vent header was 24” x 0.375” wall, and the vent outlet was 16” x 0.375” wall. The results from NozzlePRO are shown below and confirm what is generally known about these intersections. The larger footprint of the lateral improves the moment carrying capacity, but cuts a larger hole in the header in the longitudinal direction increasing the hoop stress effect. The hillside in this d/D ratio performs essentially as well as the straight through intersection.
B31.3 Calculations r2 = (0.5)(24 – 0.375) = 11.8125 rB = (0.5)(16 – 0.375) = 7.8125 B
2 Ze = (π)(rB )(T)
= (π)(7.81252)(0.375)
= 71.9
io = 0.9/(T/r2)(2/3) = (0.9)/(0.375/11.8125)(2/3) = 8.98 ii = 0.25 + (0.75)(io) = 6.98 Se = (i)(M)/Ze < Sa Sa = 1.25(Sc+Sh) (SL assumed = 0 for simplicity) Let Sc = Sh = 20 ksi Sa = 1.25(20ksi + 20ksi) = 50ksi Mi < SaZe/ii=(50000)(71.9)/6.98 = 515043 in.lb. Mo < SaZe/io = (50000)(71.9)/8.98 = in.lb.
Straight Through
Lateral (45)
InPlane Max Allowed Moment 583,179 in.lb. 786,243 in.lb. Outplane Max Allowed Moment 171,867 in.lb. 304,402 in.lb. Maximum Allowed Pressure 348 psi 160 psi Note (1): For B31.1 the Inplane and outplane moments are the same.
Hillside
B31.3
451,108 in.lb. 191,997 in.lb. 326 psi
495,658 in.lb.1 385,698 in.lb. n/a
The allowable load report report from NozzlePRO lets the user directly compare fittings and geometries as was done above. An example allowable load report for one of the nozzles above is shown below. Allowable Loads SECONDARY Load Type (Range): Axial Force Inplane Moment Outplane Moment Torsional Moment Pressure
(lb. ) (in. lb.) (in. lb.) (in. lb.) (psi )
Maximum Individual Occuring 43881. 583179. 171867. 598463. 348.73
Conservative Simultaneous Occuring 11228. 105101. 30957. 145044. 100.00
Realistic Simultaneous Occuring 16841. 222953. 65671. 217566. 100.00
(lb. ) (in. lb.) (in. lb.) (in. lb.) (psi )
Maximum Individual Occuring 67023. 514214. 377181. 334385. 240.90
Conservative Simultaneous Occuring 17594. 72906. 51998. 66047. 100.00
Realistic Simultaneous Occuring 26391. 154657. 110303. 99071. 100.00
PRIMARY Load Type: Axial Force Inplane Moment Outplane Moment Torsional Moment Pressure
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The results obtained were expected. There is not enough experience with hillside nozzles yet to draw any conclusions from the above results. Tests and Code data produced to date cover too limited a scope to permit any general conclusions to be drawn.
Example 4 – Rectangular Attachments (WRC 107): As might be expected, WRC 107 for a rectangular attachment that has essentially the same dimensions in the longitudinal direction as the 8” pipe above produces essentially the same stress. The FEA model shows higher stresses around the corners of the geometry where the stress is concentrated. The FEA model also shows the beneficial effect of pads, and the gross errors that can occur when WRC 107 is used for pad type attachment geometries. WRC 107 Pad Lug Edge(2) Edge(1) 141,818 n/a 43,215 90,929 43,215 34,639 43,215 22,619 43,215 22,619 43,215 22,619
Line Load(3) Lug Pad Edge(1) Edge(2) 111,139 n/a 39,462 67,989 39,462 24,909 39,462 15,619 158,145 15,619 299,006 15,619
6x8 Rectangle No Pad 6x8 Rectangle 1” Wide Pad 6x8 Rectangle 4” Wide Pad 6x8 Rectangle 6” Wide Pad 6x8 Tri Plate Supt. 6” Wide Pad 6x8 Inverted Tee 6” Wide Pad Notes: (1) Simulated by increasing vessel thickness. (2) Simulated by increasing Load Bearing Area. (3) Ref: H. Bednar, Pressure Vessel Design Handbook, Van Nostrand, New York, 1981.
Geometry: Vessel
FEA Lug Edge(1) 129,813 71,197 46,775 41,299 42,311 75,275
Pad Edge(2) n/a 70,604 30,960 24,257 24,358 24,631
ID = 72” T=0.625”
Loads: Longitudinal Moment = 45000 ft.lb. (540,000 in.lb.)
Rectangular Attachments in 5 Steps Step 1 of 6 Start Nozzle/PRO by double-clicking the desktop Short/Cut Step 2 of 6 Select Input Units (English or SI) For this example select “English” units
Step 3 of 6 Select a “Base Shell Type” and input “Vessel” Dimensions In this example select “Cylinder” and input the vessel OD and wall thickness
Copyright (c) 2007 by Paulin Research Group
1.4.11
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Step 4 of 6 Select a “Nozzle/Attachment Type” and input the dimensions In this example select “Structure 6” and input the Structure dimensions.
Note these inputs are described in the images below
Step 5 of 6 Select “Loads” and input the loads and/or monments In this example input 45000 in the MZ (ft.lb.) and click O.K.
Step 6 of 6 Run and Review Results Click “Run FE”. Once the analysis is complete, Nozzle/PRO will display a message indicating the run has finished.
The results discussed above clearly demonstrate that care must be taken when using WRC 107 for pad reinforced structural attachments. Depending on how the analyst views the WRC 107 evaluation of the connection significant errors could be made. The value (RT)1/2 should be used as the minimum pad width if at all possible, (where “T” is the sum of the pad and header thicknesses.) (WRC 297 recommends using the value 1.67(RT)1/2) (RT)1/2 is the width of the pad away from the nearest edge of the structural attachment. For rectangular shapes, running the support plates right up to the edge of the pad completely eliminates the repad usefulness. Inverted tee supports Copyright (c) 2007 by Paulin Research Group
1.4.12 12
NozzlePRO
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produce twice the stress of the rectangular plate supports, which more evenly distribute the stress over the pad. NozzlePRO is particularly useful at evaluating the stresses due to different geometric shapes. Only the single structural type parameter needs to be changed to alter the support cross section: are automatically distributed evenly over the outer section of any cross section selected.
Box (no Pad) (129,813)
Box (1” Pad) (71,197)
Box (6” Pad) (41,299)
Triple-Plate (42,311)
. The entered loads
Box (4” Pad) (46,775)
Inverted Tee(75,275)
Example 5 – Using FE/Pipe and Nozzle/PRO SIFs in Pipe Stress Programs: ASME B31 SIFs published in 1955 were determined experimentally using tees having the same branch diameter and thickness as the header diameter and thickness (d/D = 1 and t/T = 1). The ASME later (1965) introduced a correction factor for branch stresses when d/D < 1. The original SIF equations are still used by the codes: io = (0.9)[(tH)/(RmH)]2/3. > 1.0 ii = (0.675) [(tH)/(RmH)]2/3 + (0.25) > 1.0 FE/Pipe and Nozzle/PRO Stress intensification factors use the WRC 329 definition of “if”, or “ifailure”: These SIFs are based on the actual nozzle section modulus and do not require adjustment for branch connections smaller than the header. For example:
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1.4.13
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Comparing SIF usage for Expansion Stress, SE Using “Appendix D” SIF ASME B31.1 For (0.75ioB31)(tB)/(tH)<1.0 For (0.75ioB31)(tB)/(tH)>1.0 ASME B31.3 For (ii)(tB)/(tH) < 1.0 For (ii)(tB)/(tH) > 1.0
Using “FE” SIF
[Mi2 + Mo2 + Mt2]0.5/( π RmB2 tB)
(ioFE)[Mi2 + Mo2 + Mt2]0.5/( π RmB2 tB)
(ioB31) [Mi2 + Mo2 + Mt2]0.5/( π RmB2 tH)
(ioFE)[Mi2 + Mo2 + Mt2]0.5/( π RmB2 tB)
[Mi2 + Mo2 + Mt2]0.5/( π RmB2 tB) [(ioB31 Mo)2+(iiB31 Mi)2+Mt2]0.5/(πRmB2tH)
[(ioFE Mo)2+(iiFE Mi)2+(Mt)2]0.5/(πRmB2tB) [(ioFE Mo)2+(iiFE Mi)2+(Mt)2]0.5/(πRmB2tB)
B
B
B
B
B
B
B
B
B
B
Under certain conditions pipe stress programs do not distinguish between test SIFs (“if”) and B31 SIFs. If the pipe stress program adjusts the FE/Pipe SIFs, bending stress in the branch will be under predicted by the ratio (tB/tH). The following graph puts this in terms of actual pipe sizes: error is plotted is for standard thickness branch connections on a 20inch std. wall header. B
...Numerical Example: NPS 20 x 4 un-reinforced branch connection (std wt, all) Shell Type: Diameter Wall thickness
cylinder 20 inches 0.375 inches
Nozzle/Attachment Type: Diameter Wall thickness
Straight 4.5 inches 0.237 inches
... For SIF generation, leave all other parameters at defaults
Nozzle/PRO Branch SIFs: Inplane 4.04
Outplane 7.42
Torsion 1.43
Axial 11.63
Note: For strict comparison to the ASME B31.3 Code, the axial, pressure and torsional SIFs are ignored. For this reason pipe stress programs only match complex finite element models when the loads are dominated by inplane moments or outplane moments. When a branch connection has high axial or torsional loads or complex load combinations, the pipe stress model and the finite element calculation will predict different stresses.
Copyright (c) 2007 by Paulin Research Group
1.4.14
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Checking Pipe Stress Model It is important to understand how your pipe stress program is using Nozzle/PRO SIFs. A test model was built in Caesar II to illustrate how FEA SIFs can be incorrectly applied. Later it is shown how to adjust Caesar’s input to get the correct result. To make verification easier, only a single moment is applied to a simple system shown in the figure below. Using the same diameters and thickness, the remaining Caesar II model details are as follows (1) All three elements are 40” long. (2) The intersection is defined as an “un-reinforced tee” with user input SIFs (3) A concentrated in-plane moment of 2685.8 ft-lb is applied to node 40 (no pressure, no weight, etc). (4) The only restraint in the model is the anchor at node 10
Manual calculation of ASME B31.3 expansion stress: Se = (ii)(Mi)/Z = (4.039)(12)(2685.8)/(3.214) = 40503 psi (86% of allowable stress)
Pipe Stress Program Code Compliance Report: NODE
20
Bending Stress lb./sq.in. 24327.0
Torsion Stress lb./sq.in. 0.0
SIF In Plane 4.040
SIF Out Plane
Code Stress lb./sq.in.
7.420
24327.0
Allowable Stress lb./sq.in. 50000.0
Ratio %
48.7
Caesar’s output is correctly reporting the user’s SIF, but the expansion stress is 40% lower than the manual calculation. The ratio of (tB/tH) is 0.63, which is about the same as the ratio of the stresses within rounding errors. So we know the reason for the difference is that the reduced branch intersection rules are being applied. B
The same loads input into the Nozzle/PRO model give an expansion stress (SE = PL+PB+Q+F) of 40,500 psi (plot below)... so the Caesar II result with the FEA SIF is incorrect. There are two avenues to correct this result: (1) increase the FEA SIF to counter the pipes tress program’s “Ze” adjustment, or (2) Somehow deactivate the B31 reduced intersection calculation.
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1.4.15
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Finite Element “SE” Stress Distribution Option 1: Increase SIF to Counter-act the “Ze” Correction: This option is simplest, but often conservative for header moments. Nozzle/PRO SIFs are adjusted by multiplying by (tH/tB) as shown: B
Nozzle/PRO Branch SIFs:
FEA “Adjusted”
Inplane 4.04 6.39
Outplane 7.42 11.74
Generating SIFs for loads applied through the header: Step 1 of 2: – Select the “Options” Menu:
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1.4.16
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Step 2 of 3: Select “SIF’s and K’s for Cylinder Header”
Step 3 of 3: Run Model and Review Results Nozzle/PRO Header SIFs
FEA “Adjusted”
Inplane 1.58 2.5
Outplane 0.37 (1) 0.58 (1)
SE in header: Nozzle/PRO SIF: Se = (ii)(Mi)/Z = (1.576)(12)(2685.8)/(113.433) = 447.8 psi Adjusted FE SIF: Se = (ii)(Mi)/Z = (2.494)(12)(2685.8)/(113.433) = 708.6 psi Option 2: Turn off the “Ze” correction. In Caesar II, the user can turn off the Ze correction locally by not specifying an intersection type. There are two drawbacks to this approach: (1) When the SIF type is not defined, SIFs must be defined on all three elements (2) The user must now confirm the inplane and outplane directions. Branch and header SIFs input as shown (per intuition), give a correct branch stress, but not a correct header stress.
element 10-20
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element 20-30
element 20-40
1.4.17 17
NozzlePRO
ELEMENT
10 – 20 @ 20 20 – 30 @ 20 20 – 40 @ 20
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Bending Stress lb./sq.in. 289.5 0.0 40506.8
Torsion Stress lb./sq.in.
SIF In Plane
SIF Out Plane
0.0
1.600
1.000
0.0 0.0
1.600 4.040
1.000 7.420
Code Stress lb./sq.in.
289.5 0.0 40506.8
Allowable Stress lb./sq.in. 50000.0
Ratio %
50000.0 50000.0
0.0 81.0
Allowable Stress lb./sq.in. 50000.0 50000.0 50000.0
Ratio %
Allowable Stress lb./sq.in. 50000.0 50000.0 50000.0 50000.0
Ratio %
0.6
The same error occurs in the branch if the model is rotated 90 degrees about the x-axis:
ELEMENT 10 – 20 @ 20 20 – 30 @ 20 20 – 40 @ 20
Bending Stress lb./sq.in. 289.5 0.0 74396.0
Torsion Stress lb./sq.in. 0.0 0.0 0.0
SIF In Plane 1.600 1.600 4.040
SIF Out Plane 1.000 1.000 7.420
Code Stress lb./sq.in. 289.5 0.0 74396.0
0.6 0.0 148.8*
The correct result is only obtained by switching the SIFs from inplane to outplane: ELEMENT 10 – 20 @ 10 10 – 20 @ 20 20 – 30 @ 20 20 – 40 @ 20
Bending Stress lb./sq.in. 289.5 463.1 0.0 40506.8
Torsion Stress lb./sq.in. 0.0 0.0 0.0 0.0
SIF In Plane 1.000 1.000 1.600 7.420
Copyright (c) 2007 by Paulin Research Group
SIF Out Plane 1.000 1.600 1.000 4.040
Code Stress lb./sq.in. 289.5 463.1 0.0 40506.8
0.6 0.9 0.0 81.0
1.4.18
NozzlePRO
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Chapter 1 – Section 5 How to Get Help Help is available via email from [email protected] Submit the file .nozzlepro and a description of the problem or question along with the Serial Number ie. NP-XXXXX. One of several routes may then be pursued. If the question can be answered directly, a response will be returned immediately. If some further work is required then a different file may be returned. In general, only a small amount of mesh adjustment is ever needed, and the improved mesh is returned with instructions on how to rerun the model. If you have the latest version of FE/Pipe you can similarly operate on the existing input by moving the NOZZLE.ifu file for 3d shell models, or the SETUP.IFU file for axisymetric 2d and brick models from the OUTPUT folder into a new data directory, and then starting a new job with the name NOZZLE or SETUP. The jobname should be changed from NOZZLE and SETUP to something more meaningful to the user. d will only have to be done once.
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1.5.1
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Chapter 2 – Section 1 Getting Started, Printing Reports, and File Handling When NozzlePRO is properly unlocked it will startup as shown below: (When NOT unlocked the word DEMO will appear across the window handle on the top of the screen and input will be limited.) If the words DEMO
show up across the top of the window handle DO NOT USE the results of the PROGRAM for engineering evalutions!
Begin by selecting the base shell and nozzle or structural attachment types, the units to be used and whether or not the shell material should be the same as the nozzle material. Once these inputs are chosen, for a straight nozzle in a cylindrical shell the main NozzlePRO form will appear as shown below:
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2.1.1
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Only the text fields described by black labels are required. Blue text labels are optional. Enter a 20 inch outside diameter cylinder with a 1.0 inch wall, and a 10 inch diameter nozzle with a 1.0 inch wall. This input is shown below:
Click on the Loads button, and then enter a pressure of 100 psi. Leave the rest of the fields blank.
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Click OK, then click the Plot Only button on the main form. A separate window with the plotted finite element model should appear on top of the main plot form as shown below.
The model should now be ready to run. Close the plot window by using the in the upper right corner of the plot window, or by using file:close. From the main form click on Run FE. A data check will be performed and the following dialog box should appear:
Click on OK, and depending on the speed of your machine the run will take between 1-to-10 minutes. A status bar will be shown in the middle of the main form, and plotted results will show up intermittently. When the run finishes the two bottom panels on the main form will be replaced by a web browser window with the NozzlePRO output displayed.
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2.1.3
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The output appears in three separate browser panes. The form may be maximized to get a better view of the output. Additionally the user may select “Graphical Results” from the leftmost pane (on the bottom in the image above), and a separate browser window will be brought up that contains only the graphical results. (The user can then toggle back and forth between the graphical and tabular results windows.) The vertical bar in the middle of the three panes can be moved using the mouse so that the full tabular results screen can be shown. The image below shows a maximized window with the tabular results bar stretched to the right and font size “4” selected. The tabular results have been scrolled down to the ASME Overstressed Areas Report.
Separate buttons appear with each graphical plot that let the user invoke a 3-dimensional view of the stress state displayed. The “3d Deformed” view of the pressure (Pl) stress state is shown below: Copyright (c) 2007 by Paulin Research Group
2.1.4
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The 3d viewer was designed to let the user “hold the dynamically moving model” in his or her hand. The stress state may be rotated, zoomed, clipped, scaled or a thermometer may be used to selectively view the actual value of the stress state. If the load case selected has an associated displacement case, then the model will be shown dynamically displacing. The style of the dynamic displacement can be adjusted using the cockpit controls on the right side of the window. The 3d viewer uses DirectX technology. Version 7.0a or later of DirectX must be loaded on the host machine. (Windows2000 loads version 8.0 as part of the operating system.) Hold the left mouse button down and move the mouse to rotate the geometry. Dragging the right mouse button “pans” the geometry. The 3d Viewer is discussed in more detail below but is designed to be “played-with.” Users are encouraged to test the different features to get a “feel” for what works best for them. Each output report is discussed in detail in the Output Review section below. Hopefully, a good portion of the key is shown NozzlePRO input and output is self-explanatory. Where help is available on an input form a next to the input text box. An example form with help, and the associated help window is shown below:
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2.1.5
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Most of the input for the default 3D shell calculation is self-explanatory. Particular items of engineering interest are discussed below. Input for Axisymetric brick and 2d element models are described later.
Load Definitions: Operating loads should include the weight loads. The operating loads are the total loads that act on the intersection through the branch or attachment in the operating condition – usually the thermal plus pressure plus weight load case. Loads are applied at the end of the nozzle or attachment and are typically the values that would be read directly from a pipe stress or structural steel program. These loads do not include the P*A axial component due to pressure for pipe. The P*A load is included automatically by NozzlePro in addition to any other loads applied to the pipe nozzle. Loads are distributed across the structural attachment cross-section end in a manner consistent with the beam analogy. (Users do not have to be concerned with boring degrees of freedom, torsional moments, or shear loads causing excessive bending in the structural shape. Vertical shear loads are distributed over longitudinal plate members, for example. Moments on structural attachments are provided as a force couple where practical or as a linearly varying force over single members. NozzlePRO calculates the difference between weight and operating loads as the “range” case required as part of the ASME Code secondary stress shakedown evaluation procedure. The difference between the weight and operating loads is also used to find the cyclic stress and is used in the ASME Code fatigue analysis. If there are significant weight and pressure loads but no thermal loads then the operating and weight loads should be the same. In this case the only load quantity causing cyclic stress is pressure – and pressure must cycle at least once. The ASME Section VIII Division 2 Code directs that occasional loads should be combined with weight, pressure and other mechanical loads, and that the resulting stresses should be compared to 1.5(k)(Sm), where k=1.2, and Sm is the hot allowable for the material. The user should leave the Occasional Cycles data cell blank or zero to effect this evaluation. (The Occasional Cycles data cell is found on the Advanced Options Screen.) When the Occasional Cycles data cell is blank or zero the occasional load entered should be the largest signed component of the occasional load. In general this is the magnitude of the wind or earthquake load. NozzlePRO will treat the occasional load as a fatigue-causing load only if the user enters the number of occasional cycles. In this case the user should enter the number of occasional cycles and the full range of the occasional loading. Whenever NozzlePRO sees a nonzero number of occasional cycles it treats the occasional load as a full range cyclic load component. Earthquake loads, for example, are often evaluated as fatigue causing loads with 100 cycles. To evaluate an earthquake load as cyclic, the user should enter the full range of the load, usually twice the value from a static seismic pipe stress analysis.
Geometry:
The user should always check the mesh produced by NozzlePRO before running a job. The element grid should be reasonably uniform without holes, doubled over areas, or obvious geometric anomalies. If the output is reasonable, the mesh typically is too. A wide variety of geometries have been tested with the NozzlePRO mesher, but certain constructions may still cause errant meshes. A large number of mesh control options exist wit7•h version 4.0 of NozzlePro, but users suspecting mesh related problems are encouraged to email the model to [email protected] (The model file is stored as .nozzlepro.) After only a little experience reviewing finite element results users will have sufficient experience to know when results are errant and due to mesh-related problems. For spherical, elliptical, dished and conic heads, and for cylindrical geometries with structural attachments, the user can optionally use the unstructured mesher. Structured meshes are preferable, but in certain cases unstructured meshes produce better results. A comparison between structured and unstructured meshes is shown below:
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2.1.6
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The unstructured mesh option and several other mesh controls are available on the Options form:
The Crude Mesh check box will cause the program to use the coarsest mesh possible. The Opt. Mult box lets the user enter a value that will multiply the default mesh. Any value greater than 0.01 may be entered but users are cautioned against inputing values much greater than 2. (Usually values of 1.5 to 1.8 work best.) As a rule of thumb, the element side length immediately adjacent to a discontinuity should be smaller than (RT)1/2, where R is the mean radius and T is the thickness. (This is the side of the element that is pointing away from the discontinuity. Element sides parallel to the discontinuity can generally be larger. The required size of the element is a function of the variation in the stress/deflection state.) For head geometries the straight flange, transition and shell lengths can be omitted if desired, but it is recommended that at least (3)(RT)1/2 of shell length be added to any head boundary. Conversely – just because there is 20ft. of 48” diameter shell attached to a 48” diameter head – there is no reason to enter 20 ft. of shell. Usually only 3- to 4- times (RT)1/2 needs to be entered down the shell length to accurately trap discontinuity stresses in the vicinity of a nozzle or attachment on the head. When the d/D ratio is large, the nozzle may distort the cross section of the head and this distortion will extend down the shell. An accurate attached shell length must be entered to properly observe this effect. Nozzle tilt angles can only be entered for cylinder or cone geometries, or for head geometries where the nozzle is off the centerline of the vessel by more than the diameter of the nozzle. The NozzlePRO and underlying geometry evaluation software make every attempt to create a viable geometry for analysis. Where assumptions or adjustments to the user’s input are made notes are printed in the Model Data report. This report should be reviewed closely for proper interpretation of the user’s data. Copyright (c) 2007 by Paulin Research Group
2.1.7
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Printing Reports: The Print button is activated whenever a finite element report is displayed in the browser. When the user clicks the Print button the contents of each pane are sent to the printer. (The target printer can be defined when the Windows Print Panel appears.) If the user only wants tabular reports he can right click in the tabular reports frame and then click on the Print menu selection that appears in that frame. Plotted results can only be copied to the clipboard and then “Pasted” into another document. The 3D viewer images can be sent to the clipboard by selecting Edit:Copy Image to Clipboard. The image can then be “pasted” into another document. The lighting in the 3d viewer can be adjusted to produce stunning images of the deformed and stressed model state.
The small numbers under the Print button: are used to size the print. Selecting a larger number results in the use of a large font in the tabular reports so that it can be seen easier on the screen. Selected parts of the text reports can also be highlighted and copied to the clipboard by left clicking and dragging the mouse over the desired text to highlight it. Once the desired text is highlighted, the right mouse button can be used to copy the text to the clipboard.
Files: NozzlePRO has a somewhat unusual file system because of the variety, use, and size of the data files manipulated. The “Files” button in the middle-right of the main data screen is used to access the file system manager.
The input for Nozzle PRO is stored in the current data subdirectory under the filename .nozzlepro. The current subdirectory is always shown in the title bar of the NozzlePRO window. If the user does not enter a current subdirectory or name, then the subdirectory name NOZZLE will be chosen and established under the application root directory. Output is stored in an “OUTPUT” subdirectory under the data subdirectory when the FEA calculation completes. The data directory is cleared when the job finishes unless the user asks for intermediate data files to be retained. The only files needed to browse output are in the OUTPUT folder. The file structure is shown schematically below:
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2.1.8
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When starting a new job it is best to establish the name for the datafiles where the job will be stored. Enter the new jobname in the “Input Filename:” textbox, and then click on Make “Input Filename” Current., then click on “Finished Here.” The new filename and current folder should appear in the window handle of the main form.
Version 4.0 of NozzlePRO allows the user to Edit the FE/Pipe input file, and it allows support engineers to send FE/Pipe input files back to NozzlePRO users. The FE/Pipe input file for shell models is NOZZLE.ifu and for axisymetric 2d or axisymetric brick models is SETUP.ifu. To circumvent the standard NozzlePRO file handling sequence an already existing IFU file can be placed in the subdirectory to be read in place of a new one. The “Use Existing FE/Pipe Input File” checkbox must be checked on the optional data form before the file will be used.
When each job is finished, the used IFU file is written to the OUTPUT subdirectory for storage. (Everything in the subdirectory is automatically deleted when the job is completed unless the user checks the checkbox to Leave FE/Pipe data files.) For the “smithco2” job above, the FE/Pipe input file would be found in the file smithco2OUTPUTNOZZLE.IFU after the run. If a support engineer emailed a modified NOZZLE.IFU file back to the user it would be placed in the subdirectory, (e.g. smithco2NOZZLE.IFU) and the “Use Existing FE/Pipe Input File” checkbox would be checked so that the ifu file would be recognized and used for the subsequent run. (The IFU file is written by NozzlePRO whenever a model is plotted or run. If an IFU file already exists in the smithco2 folder and the Use Existing FE/Pipe Input File box is checked the old ifu file will be used. This is what we want if a change is made to the IFU file that should continue to be used. This is NOT what we want 99% of the time when NozzlePRO is being run in a standard mode outside of the FE/Pipe interface.) This is a convenient feature for FE/Pipe users. They can build the base model in NozzlePRO to take advantage of its smart mesh algorithms. They can use the FE/Pipe data editor to enhance the model, and then they can get the standard NozzlePRO output for reporting. A typical file structure is shown below: Data File Example Structure
Input datafile for Job N102: Intermediate Data Files: FE/Pipe Input File: FE/Pipe Input File: Output Browser Files: Output Static Plots Output 3d Models
C:SmithConsultingN102.nozzlepro C:SmithConsultingN102*.* C:SmithConsultingN102NOZZLE.IFU...put it here to use in NozzlePRO. C:SmithConsultingN102OUTPUTNOZZLE.IFU ... found here when job finishes C:SmithConsultingN102OUTPUTNOZZLE*.HTM C:SmithConsultingN102OUTPUT*.BMP C:SmithConsultingN102OUTPUT*.fex
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2.1.9
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Output 3d Results
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C:SmithConsultingN102OUTPUT*.fea
The output HTM and BMP files are written in standard file formats that can be read by any HTML browser. The standard htm files for a 3d shell model are shown and described below. (Files with the “p” prefix do not include the directX buttons .) For 2d axisymetric models the name NOZZLE is replace by the name SETUP. NOZZLE-toc.htm – Table of contents for graphic pictures. NOZZLE.htm – Body of text output report. NOZZLE-frame.htm – 3 frame htm setup file. (Point your browser to this file to get the nozzlePRO 3 frame output window just like you see it in NozzlePRO with the directX buttons displayed and active.) NOZZLE-pics.htm – Body of graphics output report that contains directX buttons displayed and active. NOZZLE-pframe.htm – 3 frame htm setup file that does NOT include the directX buttons displayed and active. (See the figure below for an example of what the directX buttons look like.) NOZZLE-ppics.htm – Body of graphics output report that DOES NOT contain the directX buttons. (This is the htm report used for printing.) NOZZLE-ptoc.htm – Table of contents for report that includes directX buttons. An example frame with the directX buttons INCLUDED is shown below:
The bmp files can be used in Microsoft WORD or any document processor. The 3d model output files can only be used with the Paulin Research Group 3d viewer. This is a nonprotected program which may be distributed freely by licensed NozzlePRO customers to their own clients for the purpose of viewing 3d results. The only job files that need to be delivered are the fex and fea files. To deliver the viewer, the files VIEWFE.EXE, DXLIB7.DLL, DXLIB8.DLL and PARTICLES.TGA must be included. When VIEWFE starts, the user may navigate between data sets to show any combination of results. VIEWFE requires that DIRECTX 7.0A or later be loaded on the host machine. Windows 2000 and XP includes DIRECTX support automatically. Windows 98 or 95 users can download DirectX from the Microsoft web site. Windows NT users must upgrade to Windows 2000 to use the 3d viewer. The test platforms at PRG are Windows 2000, Windows XP, and Windows 98.
Copyright (c) 2007 by Paulin Research Group
2.1.10
NozzlePRO
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Chapter 2 – Section 2 Common Load Types and Categories Primary Loads. Loads The nature of Primary Loads is that the load magnitude does not diminish when the structure deforms.
(Weight loads are also subdivided into “Dead” and “Live” Loads in structural steel codes) Figure 1 – Primary Load Examples
Secondary Loads.
The nature of Secondary Loads is that the load magnitude diminishes as the structure deforms. Almost always these loads are a type of restrained expansion. NOTE: The designer must be aware that this definition is temperature dependant. At temperatures in the creep range of the material, some secondary loads take on the characteristics of PRIMARY loads.
(At temperatures below the creep range)
(Restrained Thermal Expansion)
(Through Wall Temperature Gradient) Figure 2 – Secondary Load Examples
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Occasional Loads.
Occasional loads are similar to Primary Loads in that the magnitude of the load does not diminish with deformation. Occasional loads are distinguished from Primary Loads by being generally “rare” short duration events rather than continuous loads.
Wind
Acceleration (e.g., FPSO or Seismic) Figure 3 – Occasional Load Examples
Fatigue Loads:
The only requirement of a Fatigue Load is that the load has multiple repetitions (has cycles). A fatigue load can otherwise be described under any other Load Category.
Common Stress Types The complex stress state of any component can be broken down into the following sub-components.
Shear Stress.
Shear stress is a tensor component used in the calculation of principal stresses.
Figure 4 – Shear Stress Examples
Membrane Stresses. Membrane stress is a mean stress averaged through the thickness, oriented parallel to the mid surface. Circumferential and longitudinal pressure stresses in a cylinder are shown below. Membrane stresses are tensor components used in the calculation of principal stresses. Note that in the absence of shear stresses, the magnitudes of the membrane stress tensors are often identical to stress intensities. Can also be an “F/A” type of stress.
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Figure 5 – Membrane Stress Examples ...Two Kinds of Bending Stress:
Bending Stresses.
Bending stress is term with different meanings depending on the code used or the
analytical technique used. (a) Beam bending
b = (M)(y)/(I) ... (so long as total stress < yield stress) Figure 6 – Beam Bending Stress
Beam Bending Stresses. This is a longitudinal stress. In piping codes this stress is treated as a uniform stress through the thickness of the pipe (varying with position on the circumference). Note however, that torisonal shear stresses are also included in the piping codes’ bending stresses. This is also the type of bending stress reported by beam element models. (b) Shell bending Shell Bending Stresses. This is a stress that varies through the thickness. In ASME Section VIII Division 2, this is the only bending stress explicitly defined. Examples of shell bending are shown in the longitudinal and circumferential directions below. Note that in some components, such as pipe shoes or saddles, the bending stress may be oriented in directions other than just circumferential or longitudinal. This is the type of bending stress reported by shell element FE models. Axisymmetric and Brick element model results must be post processed to this same definition.
= (6)(MO)/(t2), or (6)(ML)/(t2) ** Note: direct shear is also represented as “Q” in this figure b
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= (6)(M)/(t2) Figure 7 – Shell Bending Stress Examples b
FEA Trivia Question: How are beam bending stresses represented in an FEA model? ANS: (a) For beam elements: as beam stresses. (b) For all other element types: as membrane stresses
Peak Stresses “F”: Peak stresses are related to “notch effects” and are only important for fatigue life. If there are no load cycles, then peak stresses are unimportant (except for some special environmental considerations, like SCC).
Figure 8 – Peak Stress Example (Axisymmetric Nozzle/Shell Junction)
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Stress Categories Individual Stress Intensity Components The stress components described in Section (2) above must be calculated for separate load cases and combined to determine principal stresses for each load category. Stress Intensities are computed from the principal stresses [4120.] 1> 2> 3 S12 = || 1 - 2 || S23 = || 2 - 3 || S31 = || 3 - 1 || Stress intensity = Max( S12, S23, S31) There are code limits on some individual stress intensities such as “PL” (described below). Other code limits (see 3.2) are determined by first computed combining tensor components for membrane, bending, etc, then finding the principal stresses and stress intensities.
Primary Stresses: Pm, PL, PB Primary stress can only be caused by primary loads Primary stresses lead to burst or collapse...deformations in the structure do not reduce the magnitude of primary stresses (eg. primary stresses are not “self-limiting”.) Pm = General Primary Membrane Stress [4-112(f) & (g)] PL = Primary Local Membrane Stress [4-112(i)] Pb = Primary Bending Stress [4-112(g)] Pm is (usually) not an FEA stress: Pm is satisfied by code formulas for pressure design, except for unlisted components. Pb (as a shell bending stress) is not a stress usually found in Nozzle/PRO geometries (See Table 4-120.1, of ASME Section VIII Division 2). Note: under Section III definitions, where Pb is due to beam type bending, it is considered “conservative” to include it as “PL”.
Secondary Stresses: Q Primary or secondary loads can cause secondary stress. The following cylinder cone junction under pressure loads illustrates how primary loads (pressure) cause secondary stresses:
Figure 9 – Secondary Stress Caused by Primary Loads
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Secondary Stresses are not usually subdivided in to “m”, “L” and “b” categories under Division 2, except when the “SPS” stress limit is exceeded. (See article 4-136.7 of Division II) Nozzle/PRO’s use of “Qb” for primary loads is NOT an ASME VIII Division 2 code check, it is an ASME Section III code check.
Combined Stress Intensities and Stress Intensity Ranges The code rules and limits on combined stresses are based on preventing ratcheting. Stress intensities are computed as described in (3.1). First the code rules assume that material behaves as elastic perfectly plastic (Figure 10). The possible combinations of primary and secondary stress are illustrated in the simplified diagrams of Figure 11: the left hand side is a simplified hysteresis diagram, and the right hand side is a simplified Bree diagram. The Bree diagram is a simplified illustration of the combination of primary and secondary stresses. In the code it is possible to enter the “P” range of the Bree diagram, but there is a heavy penalty on Fatigue stresses (Article 4-136.7). The code stress combinations and limits are illustrated by Figure 4-130.1 (reproduced and amplified as Figure 12)
Figure 10 – Actual and Assumed Material Behavior
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(uni-axial hysteresis) (bree diagram) Figure 11 – Simplified Material Behavior Models
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.
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Figure 12 – ASME Figure 4-130.1 Amplified
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Nozzle/PRO Load Cases and Combinations
Nozzle/PRO Stress Reports Shell Division II Stress Type Primary
ASME B31 Stress Type Sustained
Primary + Secondary – no load to operating Primary + Secondary – installation (weight) to operating Fatigue
n/a
PL+PB+Q in PL+PB+Q out
n/a
PL+PB+Q in PL+PB+Q out
SE
PL+PB+Q+F in PL+PB+Q+F out
PL
Nozzle/PRO element type Axisymmetric Brick Smembrane, Sbend1 or Sn1. Sn Sn2 (may require manual combination of multiple models) SI
SI
Notes: (1) For axisymmetric models with pressure only Sbend and Sn, may be primary depending on location in the model. (2) For axisymmetric models with transient heat transfer, the range of stress, “Sn”, must be determined by including a separate pressure case, or by the range of stresses for different temperature cases if there is a stress reversal (check deflected shape plots). (3) Brick element models are best reviewed by using Stress/Plot
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Chapter 2 – Section 3 Options Data Form
Weld Size/SCF – The two data cells to the right are used for the weld size and the associated stress concentration factor (SCF). The SCF is only used to calculate peak stresses in 3D shell models. The weld size is only used for nozzle geometries, (not structural attachments). The Weld Size is also used for the axisymetric 2d and brick nozzle models. button to see a The weld size is the leg length of the fillet weld between the header and nozzle. Click on the drawing defining the weld dimensions. The SCF (Stress Concentration Factor) indicates the increase in peak stress due to the presence of the weld geometry and the effect of welding. Generally the SCF must come from a comparison of fatigue test results and the finite element results. For PVP geometries and the element type and intersection model used in NozzlePRO an SCF of 1.35 has been found to envelop the existing fatigue test data without undue conservatism. Pad Weld/SCF – The two data cells to the right are used for the pad edge weld size and the associated stress concentration factor (SCF). This weld size is only used for nozzle geometries with pads and is also used with axisymetric 2d and brick models.
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Base Weld Leg Size – Typically the fillet weld leg length is the same along the nozzle and the header. If this is not the case then enter the length of the fillet along the header in the Base Weld Leg text box, and the length along the branch in the Weld Size text box. This option is also available for axisymetric 2d and brick models. Free POSITIVE Cylinder End – When the Base Shell Type is Cylinder the “top” of the cylinder may be freed. Any loads through the branch will be carried by the opposite side cylinder end. This is the typical boundary condition for a vertical vessel with a large nozzle. (The top of the vessel is essentially “free,” and the nozzle loads are carried through only the supported end of the vessel. This tends to produce higher stresses.) The freed end is “capped.” See the
button contents are shown below:
Free NEGATIVE Cylinder End – Mutually exclusive counterpart to POSITIVE end free option. Calculate Pressure Stress ONLY – Click on this box to have NozzlePRO ignore all other loads except pressure. Stresses will be calculated at the nozzle/shell penetration line in an attempt to trap the peak pressure stress on the inside longitudinal plane of cylindrical geometries. This option is used typically when pressure is cycling and the user is interested in a pressure only analysis. The user might consider also increasing the SCF at the nozzle welds to 1.6. This value can be adjusted based on brick model analyses of the nozzle intersection. SIF’s for Cylinder Header – For cylindrical geometries this option produces SIF’s for loads through the header. (The default is for the SIF’s to be produced for loads through the branch.) When d/D is 0.5 or less the SIF’s for moments through the header can be considerably smaller than the SIF’s for moments through the branch. The Code default is to use the same SIF for each, severely penalizing the user when the branch is not loaded. This option allows the user to enter more realistic values for header/run SIFs. Do NOT Average Stresses – Check box to turn OFF stress averaging. Stress averaging generally produces more realistic values, especially for structural attachments, but may obscure inaccuracies in the solution. Users looking closely at solutions may want to turn averaging off to get a better view of the numerically unaided stress state. Show FE/Pipe Screens During Run – Click this checkbox to see the progress of the finite element run using the FE/Pipe status screens. These screens provide more information to the user, but also take up more screen space. Often this is used to aid in debugging a run that does not run to completion. Show Intermediate Input Plots – The model plot will be displayed when the run is starting. This is included as a visual check of the job progress.
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Show Intermediate Output Plots – The model results plots will be displayed as they are created. This is included as a visual check of the job progress. Use FE/Pipe Editor During Run – Click on this check box to invoke the FE/Pipe data editor whenever the user plots or runs a NozzlePRO job. When plot or run is selected, FE/Pipe and then pauses at the FE/Pipe input data screen main menu:
NozzlePRO builds the necessary input for
From this menu, the user can modify the input using any of the options available in FE/Pipe that are available to NozzlePRO. This is used generally by the support engineer to tweak a model, or can be used by the FE/Pipe user to make quick changes to the automatically generated NozzlePRO model. AFTER changes have been made at the FE/Pipe level, the user can continue using the FE/Pipe version of the model by checking the box Use Existing FE/Pipe Input File. Leave FE/Pipe Data Files – This check box is used in conjunction with the FE/Pipe data editor box above. To continue using the same FE/Pipe input in subsequent runs the FE/Pipe input file must not be deleted. This box is also used for debugging jobs that do not complete properly. When a job aborts in error, the last data file used may give an indication of the problem. Use Existing FE/Pipe Input File – Once the user has edited an FE/Pipe input file he may want to continue to reuse those changes in subsequent runs. Click in this check box to reruse an existing input file. Note however, that NozzlePRO level changes will not be picked up if the user is running the input at the FE/Pipe data file level. These options should only be used by experts with the program or at the direction of a support engineer. Crude Mesh – Click this checkbox to use the crudest mesh possible for a given geometry. Enter a number in the box to the right as a multiplier to override the checkbox. The number entered will multiply the standard mesh density. Values can be between 0.01 and 10. The user is suggested to use large mesh multipliers with caution. Seldom are values greater than 2.0 required, and more often 1.5 –to- 1.8 is recommended. Use Unstructured Mesh for Heads or Structure – Click on this checkbox to use an unstructured mesh for spherical, elliptical, or dished heads. (Unstructured meshes may also be used for structural attachments on cylinders, but this is only recommended for shorter cylinders, where the L/D ratio does not exceed 2.) The unstructured mesh option can be used for convergence studies and in situations where the structured, parametric cubic mesher is not well suited for the geometry. Copyright (c) 2007 by Paulin Research Group
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Do NOT Use the Unstructured Mesh – There will be occasions where NozzlePRO will elect to use the unstructured mesher instead of the structured mesher. If the user would prefer to try to use the structured mesher, they can deactivate the unstructured mesher use. This is NOT recommended, and users activating these options should check the resulting element mesh and results carefully. Deactivate Element Smoothing– In certain instances the movement of nodes to form better elements results in element area overlap. Deactivate element smoothing if it is suspected that smoothing is causing this problem. This most often occurs when crude models are run. The crude model meshes are very bad to begin with, and often don’t smooth particularly well. Print Stress Outside of Discontinuity Zone – NozzlePRO was designed to find the stress around nozzle or structural discontinuities in cylinders or heads. The general stress state in the cylinder or head removed from the discontinuity is generally not of interest because the Code controls this value. Depending on the model type and d/D ratio stress artifacts may exist at boundary conditions that do not effect the stress at the discontinuity. These values are generally not printed in either the static stress plots that appear in the browser window, or in the dynamic 3D plots. If the user wishes to have the stress calculated in the entire model for the dynamic 3D plots, then the Print Stress Outside of Discontinuity Zone box should be checked. The graphical result is shown below. The tabular results will also be changed. A stress region removed from the discontinuity will be added to the report, and the highest stresses in this area reported. If a stress artifact exists at a boundary, it will be included in the report when the Print Stress Outside of Discontinuity Zone box is checked.
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Merge Nodes ToleranceThe following diagrams illustrate concepts and most common reasons to change the Nozzle/PRO defaults (1.1) Concepts
(1.2) Error “3241” = COLLAPSED ELEMENTS
Solution: input a smaller merge tolerance (see below)
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(1.3) Error “2010” = DISCONNECTED PIECE OF MODEL This error occurs if TOO SMALL a value of MERGE NODES TOLERANCE is input... (don’t over-do it)
(1.4) How to Change Merge Nodes Tolerance in Nozzle/PRO (in Two Steps) Step 1... select “OPTIONS”
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Step 2... input a “merge nodes tolerance” (for “English” units 0.005 usually works. For “SI” units, 0.1 usually works)
Insert Length – For nozzles that have inside penetrations enter the insert length. Insert nozzle end sections are perpendicular to the nozzle centerline. (Not all insert nozzles ends are perpendicular to the nozzle centerline. Some are contoured to the head. In this case the user should vary the input length to determine the sensitivity of the solution to this parameter. If a dependable solution relies on an accurate modeling of this contoured end section then a support engineer should be consulted.) Insert Thickness – The thickness of the inserted nozzle. Do Not Cut Hole in Header for Branch – Click this checkbox if the pipe does not penetrate the shell. Used when pipe is welded to cylinders or heads for support, and are not pressure carrying members. Branch Pressure – Enter a value if the branch pressure is different from the header pressure. Used for hot taps and some field welded pressure test connections when the hole is not removed from the header and the branch side may be pressurized.
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3D Shell Elements – The usual model of choice. Eight-noded reduced integration doubly curved shell elements will be used to model the requested geometry. These element models are considered a sizeable improvement over an equivalent WRC 107 or 297 type model of the same geometry. Shell elements do not consider through-thethickness direction stress gradients and tend to become more conservative when D/T ratios get in the range of 10 or smaller. Axisymetric Heads and Skirts – If this option is selected the user can set the axisymetric head and skirt options and additional loadings required using the Axisymetric Head and Skirt Options button that will become activated. The axisymetric modeler in NozzlePRO allows the user to study various through-thickness phenomena more closely, such as: 1) Contoured weld radii 2) Integral or non-integral repads 3) Skirt-to-head weld stresses 4) Effect of nozzle flanged end connections. 5) Head bed supports. 6) Welded-in Contoured Fittings. Saddle / Shoe Options – To access these options, the user must select either the saddle or pipe shoe attachment option in the main NozzlePRO screen. These options allow the user to modify the saddle or pipe shoe to account for tapered designs, multiple circumferential web plates, distance from head or front-end, and other many options. Self-weight, liquid head, and saddle forces may also be modeled for a complete and accurate mode of horizontal vessels.
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Chapter 2 – Section 4 Using the 3D Viewer DirectX may be thought of as Microsoft’s view of the 3-dimensional world. NozzlePRO models have been ported to this framework and a special viewer written to take advantage of this technology. Meshes, displacements and stresses can be viewed in “3d” much faster, and with a much better understanding of the result than with the prior “2d” slow-time rendering methods. The NozzlePRO viewer was written so that the user feels like he is holding the 3d stress/displacement model in his hand. 3D technologies are improving at an exponential rate. As engineers experience their power they will become ubiquitous on the desktop. Anyone with Windows 2000 already has sufficient DirectX 3d support to run the NozzlePRO viewer. Windows 98 and 95 support multimedia capability and also support DirectX 7.0a. The user must have a minimum of DirectX 7.0a to take advantage of this capability within NozzlePro. Users of Windows NT must upgrade to 2000 before using the 3d viewer. Microsoft never released DirectX version 7 for NT. Using the DirectX module, the user has access to translucent view, hidden-line mesh views, shaded views, scalable stress results, rotation, clipping, lighting options, and a data thermometer to read off the exact value from any point on the geometry. Viewing tools include zoom, pan, polyline, and “plane-view-zoom” options. If a displacement load case is associated with the stress state then the model will be showed in a dynamically displacing view. Controls for the dynamic displacement views are in the right screen cockpit. The DirectX models are available by clicking on the 3d viewer buttons in the stress report output pane. Examples of these buttons are shown in the plot below.
The resulting 3d Deformed model window that appears is shown below:
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Menu Options: File-Used to select different job names. When in the viewer the user can look at any 3d data file that resides on the machine. File also lets the user select various options, the most important of which is the rendering option for non-calculated vertices, usually weld zones. If the user is experiencing difficulties with the viewer, the options also permit deactivating hardware acceleration and shifting between directX7 and directX8 libraries. name='Submit1' value=' 3d '>
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Chapter 2 – Section 6 Errors – Aborted Runs – and DirectX Troubleshooting Running most finite element models requires the solution of very large sets of simultaneous equations. The sets of equations solved in most pipe stress programs are on the order of 100-to-10,000 equations of relatively small active column sizes. The sets involved in most finite element calculations are easily an order of magnitude larger, resulting in a squared increase in solution time and computer resource requirements. Accordingly, the user should not start a finite element calculation on anything slower than a 300 MHz. Pentium processor with at least 128 Mb of RAM, and at least 300Mb free on the hard disk. Larger and faster machines are preferable. The finite element program runs as a background application. The user will not see it on the task bar when running. The only way to “see” FE/Pipe running in the background is by bringing up the task manager under Windows NT/2000 or by hitting under Windows95 or Windows98. When looking at the displayed processes (programs) the user might see either: modgen fepre premini If any of these programs are running in the process list then the FEA program is running. All program errors should be trapped and reported. On a slower machine, (depending on the problem geometry), the solution might take upwards of 20-to-30 minutes to solve. On 500+ MHz Pentiums solutions should take only a few minutes. During solution a file: __file__.loc is maintained in the job run directory and CPU usage should be at about 80%. If there is no graphics in the output window when the job completes then most likely an error occurred and the user should find it described in the tabulated reports. There are several files that might give the user some guidance during an abnormal termination, and they are: error.log – Written if an abort occurred in the logic part of the preprocessing phase. modgen.err – Written for every job, but may contain a description of any errors that occurred during model geometry construction. input.add – If this file exists then it should contain a description of the model geometry. When a job does not complete successfully the user is encouraged to review this file thoroughly for potentially errant input. If errors in the input are found, the user should correct them and rerun the model. In any event, when a particular job aborts, the input .nozzlepro file should be forwarded to [email protected] for review. __file__.loc – Written during execution of the finite element portion of the run. This file contains the percentage of the current phase that is completed and the name of the current phase of the execution. Troubleshooting the Installation: If the software loads correctly and seems to run but does not produce the output data panes then most likely: a) Internet Explorer 5.0 or later is not correctly loaded on the machine, or b) The user has run out of hard disk space, or c) A geometry error has occurred. If the NOZZLE-FRAME.HTM does not exist in the...OUTPUT subdirectory then the job aborted or is still running. Jobs will abort if there are insufficient resources to solve the finite element problem. If you get the message that your executable has been invalidated then you will need to contact the Paulin Research Group for a more recent version of the program. If you get an error attempting to load the help, then either your version of WordPad or Word is out-of-date and needs to be updated. If you have an acrobat reader, the help documentation is also provided in a pdf file format.
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If the program aborts whenever you try to run then you should make sure that you have the rights to create folders and files in the current working directory. If you are unsure of the current working directory use the “Files” button to show you what Nozzle PRO thinks is the current working directory. If NozzlePRO will not install, then make sure that you have read AND WRITE access to the windows subdirectory. (This access is required by the MS program installer.) If the program always starts in DEMO mode after you have authorized it, then make sure your shortcut is pointing to the program STARTNP.EXE. Troubleshooting the 3d model viewer The NozzlePRO 3d models require that Microsoft DirectX 7.0A or later be installed on the machine. Microsoft describes DirectX as follows: “What is DirectX? Windows 2000 supports DirectX 7.0, which enhances the multimedia capabilities of your computer. DirectX includes accelerated video card and sound card drivers that provide better playback for different types of multimedia, such as full-color graphics, video, 3-D animation, immersive music, and theater sound. DirectX enables these advanced functions without requiring you to identify the hardware components in your computer and ensures that most software runs on most hardware systems.” Microsoft also suggests how to Troubleshoot DirectX as follows: Troubleshooting DirectX You can diagnose and resolve DirectX problems using the DirectX Diagnostic Tool and the Multimedia and Games Troubleshooter. The DirectX Diagnostic Tool helps you test the functionality of DirectX, to diagnose problems, and to configure your system to optimize DirectX performance. The DirectX Diagnostic Tool (Dxdiag.exe) is installed with DirectX. For information about using the DirectX Diagnostic Tool, click the Help button in the DirectX Diagnostic Tool. The Dxdiag.exe screen is shown below:
Click on the display tab (there may be several display tabs – check them all), and then execute the DirectDraw and Direct3d tests. If dxdiag.exe cannot be located on the computer, then on the computer does not have directx Copyright (c) 2007 by Paulin Research Group
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installed. DirectX can be downloaded from the Microsoft website for Windows 98 or 95 operating systems. (Microsoft never provided DirectX 7.0 or later versions for NT.) The 3d viewer File:Options dialog box appears below:
When the program is installed it will try to use DirectX8. If DirectX8 is not installed it will shift to DirectX7 automatically and ask you to restart the program. If you don’t have DirectX7 or 8 loaded then you cannot use the 3d viewer. Several other items should be checked if there is 3d viewer abnormal behavior: 1) Make sure that you have the latest drivers for your video card. 2) Make sure that you have any patches for DirectX. 3) If you have DirectX7 – try loading DirectX8. 4) If you have DirectX8 – then try switching to DirectX7 in the dialog box above. (8 supports 7). 5) Try disabling hardware acceleration in the dialog box above. 6) If none of these help, then odds are that trying the same on another, different machine WILL work. DirectX technologies attempt to get the most out of the video performance on the machine. Older versions of BIOSs, drivers or chip sets may produce erratic behavior. Usually moving to another machine will solve the problem. Some machines use hardware that is too new, and has not been adequately tested with DirectX. Some older machines have the same problem. This will be an ongoing nuisance as hardware and software changes continue at such a rapid pace. Two types of 3d geometry files are created by NozzlePRO, and each is stored in the OUTPUT subdirectory on job completion. The NOZZLE”n”.FEX file contains shaded images of the model for each load case analyzed. NOZZLE”n”.FEA files contain stress results for the different stress types for the different load cases, e.g. (NOZZLE1.FEX and NOZZLE3.FEA.) These files are registered file types with the operating system and are associated with the program VIEWFE.EXE. When the user clicks on a 3d button, or double clicks on the file directly, the 3d viewer should start and display the corresponding image. These file types are registered with the operating system during each program startup. If there is an error the user will be notified at that time. The file type registration can be checked by double clicking on “My Computer:... Folder Options ... File Types” The user may have to hunt for the “Folder Options” button in the My Computer menu as it appears in different places depending on the operating system. When the “File Types” button is clicked, the user should scroll down the file_types window that appears until the Finite Element Analysis and Finite Element Mesh files are found. This display on a Windows 2000 Operating system is shown below, (it is different on a machine with another operating system.)
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Search for the “Edit File Type” button, (again, could be in a variety of places depending on OS), Click on “Edit” or otherwise check the location of the application used to perform the “open” action. An example of this screen is shown below:
The application path and name should be the current version of the viewer. If not, then it should be changed.
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2.6.4
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Chapter 2 – Section 7 FE/PIPE, NozzlePRO, PVElite, and CodeCalc Using the FE/Pipe Input Editor: In the Options form (shown below), click on “Use FE/Pipe Editor During Run.” When this checkbox is marked the FE/Pipe data editor will be displayed prior to any plot or run. The user familiar with FE/Pipe can then make any changes needed to the input and continue on in the normal run sequence with NozzlePRO. This option is used most often under the direction of a support engineer to tweak an otherwise unwieldy model. FE/Pipe users often find generating models in NozzlePRO (especially structural models), convenient, and so use this feature to build their FE/Pipe input file. The FE/Pipe Editor can also be used to view certain geometry errors that are not trapped by NozzlePRO. The user can enter the FE editor and then “plot” the model from the editor data screen. In some cases error messages will be seen here that were not reported otherwise. The user can also check all three of the boxes shown below on the Optional data form. The FE/Pipe editor can then be used to edit and run the model data. The FE/Pipe input file will be saved and the user can continue running the modified data. User’s should only beware that changes made in the NozzlePRO forms will not take effect when running in this mode.
The recommended procedure for running in this mode follows: 1) Check the Use FE/Pipe Editor During Run and Leave FE/Pipe Data Files boxes. (See above.) 2) Make sure all NozzlePRO input is as close as possible to the desired model. 3) Click Run FE. 4) When the FE/Pipe editor appears make the necessary changes to the model. 5) Select the option SUBMIT for Analysis to exit the FE/Pipe data editor. The run should continue through to completion if an editing error was not made. 6) The standard NozzlePRO results will appear. 7) To prepare for a second run check the box “Use Existing FE/Pipe Input File” on the Options data form. 8) Click Run FE. You will now be put back into the FE/Pipe data editor with the old input. This can now be modified for a second run. Using a NozzlePRO ifu file in FE/Pipe: FE/Pipe input from NozzlePRO for 3d shell elements is stored in the file NOZZLE.IFU. This file is found after a run has completed in the OUTPUT subdirectory. This file may be read into FE/Pipe and used normally if the latest version of FE/Pipe is installed on the computer. The FE/Pipe input from NozzlePRO for axisymetric 2d and brick models is stored in the file SETUP.IFU also in the OUTPUT subdirectory. To use NozzlePRO with PVElite and CodeCalc several things must happen: 1) You must have a licensed and validated copy of the program. (You should receive a site key and be able to run NozzlePRO outside of PV Elite or CodeCalc as described in this manual.) 2) You must tell PVElite or CodeCalc where NozzlePRO is loaded. Enter PVElite input menu, choose component analysis module, that will launch CodeCalc, then under the CodeCalc tools menu, select configuration, then choose miscellaneous app, and there set the path to the folder where nozzlePRO is installed. This will store the path for all future runs and will only have to be done once.
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Chapter 3 – Section 1 Output Review for 3d Shell Models The general browser output screen appears below:
When first reviewing output always scroll through the plots to be sure that the graphical results “look reasonable.” Several examples are given later of results that do not “make sense,” and should be discarded. The buttons: can appear in any combination and indicate that 3d rendered images of the geometry or stress state are available. The 3d rendered images may be interactively rotated, panned and zoomed. Additionally a thermometer (which appears in the toolbar) can be used to read off the exact value of the stress at any point in the geometry. The 3d rendered images provide the best way to inspect the calculated stress state. These plots should be inspected at least once for each run to be sure the results “make sense.” Distorted shapes are highly exaggerated but may be scaled using the scale text box and the set scale button. The available Output Reports are listed and described below: Model Notes – Echoes the model input and gives guidance FE/Pipe Load Case Report – Describes which load cases were setup and run to satisfy Code requirements. ASME Overstressed Areas – Any areas in the model that show to be overstressed are summarized here. Highest Primary Stress Ratios – ASME Section VIII Div.2 primary stresses and allowables. (sustained) Highest Shakedown Stress Ratios – Secondary (non-peak) stresses and allowables. Highest Fatigue Stress Ratios – Expansion/peak stresses and allowables. Copyright (c) 2007 by Paulin Research Group
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Computed Stress Intensification Factors – SIF’s for use in pipe stress programs. Allowable Loads – Allowable operating, expansion and sustained loads. Flexibilities – Point stiffnesses that would be put back in a beam-type pipe stress program. FE/Pipe Load Case Report Example: A brief explanation of why the load case was set up is included before each load case. Referenced Code sections are included. FE/PIPE Load Case Report Inner and outer element temperatures are the same throughout the model. No thermal ratcheting calculations will be performed. THE 1
7
LOAD CASES ANALYZED ARE:
Sustained Sustained case run to satisfy Pl<1.5Sm limit, and Qb, the bending stress due to primary loads must be less than 3Smh as per Note 3 of Fig. NB-3222-1, and Table 4-120.1 /-------- Loads in Case Pressure Case 1 Force Case (Weight)
2
Operating
1
(Fatigue Calc Performed)
Operating case run to compute the extreme operating stress state to be used in the shakedown and peak stress calculations. /-------- Loads in Case Pressure Case 1 Force Case (Operating) Thermal
2
ASME Overstressed Areas Example: Hopefully the overstressed areas report contains the note shown here that there are NO overstressed areas in the model. If it doesn’t, the stresses that were found to be in excess of the code allowables for each region of the model are listed. ASME Overstressed Areas **** NO ASME OVERSTRESSED AREAS IN THIS MODEL ****
Highest Primary Stress Ratios Report Example: This is the sustained, or “weight plus pressure” case in general. This case is run to guard against collapse or excessive distortion. Usually pressure is the largest component of the stress. This report is used for pressure design of intersections and can be used to compare against the validity of the Code’s area replacement rules. See Code Case 2236. This is equivalent to the piping engineer’s “sustained stress” report. Highest Primary Stress Ratios Branch at Junction Pl 12,969 psi
1.5(k)Smh 22,500 psi
Primary Membrane Load Case 1 Plot Reference: 1) Pl < 1.5(k)Smh (SUS,Membrane) Case 1
57%
Copyright (c) 2007 by Paulin Research Group
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Highest Secondary Stress Ratios Report Example: This report is used to insure that local (non-peak) stress states shakedown to elastic action and do not incrementally strain ratchet. (See Bree Diagram – “Design Methods for Power Plant Structures,” David Burgreen, Arcturus Publishers.) Highest Secondary Stress Ratios Header at Junction Pl+Pb+Q 6,427 psi
3(Smavg) 52,500 psi
Primary+Secondary (Outer) Load Case 2 Plot Reference: 4) Pl+Pb+Q < 3(Smavg) (OPE,Outside) Case 2
12%
Highest Fatigue Stress Ratios Report Example: This requirement is used to ensure that fatigue crack propagation does not cause component failure at any time during its lifetime. Notice that the number of allowed cycles is given for the computed peak stress. Highest Fatigue Stress Ratios Header at Junction Pl+Pb+Q+F 19,338 psi
Sa 45,711 psi
Primary+Secondary+Peak (Outer) Load Case 2 Stress Concentration Factor = 1.350 Strain Concentration Factor = 1.000 Cycles Allowed for this Stress = 153234.0 'B31' Fatigue Stress Allowable = 43750.0 Markl Fatigue Stress Allowable = 41701.0 Plot Reference: 6) Pl+Pb+Q+F < Sa (EXP,Outside) Case 2
42
Computed Stress Intensification Factor Report Example: The inplane and outplane stress intensification factors (SIF’s) listed in the peak stress category should be put back into a pipe stress program at the section in the piping model that corresponds to the given diameter and wall thickness. SIF’s are cross section dependent! If a given SIF is less than 1.0 then 1.0 should be used. The computed SIF’s are intended to be used for the branch or nozzle piping only and can (and should) be used in conjunction with the proper flexibility for the intersection. Computed Stress Intensification Factors Branch/Nozzle Sif Summary
Axial : Inplane : Outplane: Torsion : Pressure:
Peak 1.213 1.548 2.605 0.916 6.494
Pipe OD : Pipe Thk:
24.000 8.000
Primary 1.162 1.451 2.451 1.102 6.068
Secondary 1.798 1.812 2.896 1.357 9.250
in. in.
Allowable Loads Report Example: The conservative simultaneous occurring loads should be used as a guide to limiting PRIMARY and SECONDARY loads on nozzles and branches. The sustained case loads from a pipe stress run should be compared to the PRIMARY conservative simultaneous allowable loads, and the operating and expansion case loadings from a pipe stress program should be compared to the SECONDARY conservative simultaneous allowable loads. Note that the PRIMARY maximum individual occurring pressure can be taken as the finite element equivalent of the MAWP for the intersection. Allowable Loads SECONDARY Load Type (Range):
Maximum Individual Occuring Axial Force (lb. ) 398030. Inplane Moment (in. lb.) 5306513. Outplane Moment (in. lb.) 3358105.
Copyright (c) 2007 by Paulin Research Group
Conservative Simultaneous Occuring 120631. 1137199. 719650.
Realistic Simultaneous Occuring 180946. 2412363. 1526608.
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Torsional Moment (in. lb.) Pressure (psi )
PRIMARY Load Type: Axial Force Inplane Moment Outplane Moment Torsional Moment Pressure
(lb. ) (in. lb.) (in. lb.) (in. lb.) (psi )
2343568. 344.
Maximum Individual Occuring 618455. 5998639. 5458219. 2938301. 422.
710264. 111.
Conservative Simultaneous Occuring 178300. 1222872. 1182725. 847110. 111.
1065396. 111.
Realistic Simultaneous Occuring 267450. 2594104. 2508939. 1270665. 111.
Flexibilities Report Example: These are the stiffnesses of the point springs that should be placed at the intersection of the branch with the vessel or header surface in a pipe stress program. The two translational stiffness directions not given should be entered into the pipe stress program as rigid. Axial Transverse Stiffness = 4107916. Inplane Rotational Stiffness = 23134282. Outplane Rotational Stiffness = 15084985. Torsional Rotational Stiffness = 123430323. in.lb./deg.
Copyright (c) 2007 by Paulin Research Group
lb./in. in.lb./deg. in.lb./deg.
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Chapter 3 – Section 2 Stresses and Allowables Whenever the user enters weight, operating or occasional loads, the program generates a variety of load cases designed to satisfy the ASME Section VIII Division 2 Code requirements. Weight, primary, operating, thermal, occasional and “range” load cases and allowables are established as needed. The user will find the results of this activity in the tabulated reports in the left pane of the output window. • • • • •
ASME Overstressed Areas Highest Primary Stress Ratios Highest Shakedown Stress Ratios Highest Fatigue Stress Ratios Highest Occasional Stress Ratios
If the stresses in each of these reports are less than the given allowables, then at least one portion of the Codes requirements have been satisfied. The load cases set up by the program are described in detail in the “FE/Pipe Load Case Report.” Always review the graphical results along with the necessary tabular results! Graphical results that “make sense” are a confirmation that the tabular finite element results are correct. Incorrect or invalid tabular results are almost always accompanied by incorrect, inconsistent or invalid graphical results, and graphical errors are much easier to spot! Finite element results are directly comparable to WRC 107 or WRC 297. Membrane stresses in WRC 107 or WRC 297 are directly comparable to Pl type membrane stresses from a finite element calculation. Membrane plus bending stresses from WRC 107 and WRC 297 are directly comparable to a (Pl+Pb+Q) outer-fiber stress from a finite element calculation, and peak stresses (those that include a “stress concentration factor”) are directly comparable to a Pl+Pb+Q+F alternating peak stress from a finite element program. With respect to the piping codes, (Pl) from ASME Section VIII Division 2 is approximately equivalent to the sustained stress from a pipe stress program, and (Pl+Pb+Q+F) is equivalent to the expansion stress from a pipe stress program. (Although the sustained stress from a pipe stress program can be interpreted many ways – see “Background for the ASME Nuclear Code Simplified Method for Bounding Primary Loads in Piping Systems” by S.E. Moore and E.C. Rodabaugh.) The following caveats should be noted: 1) Elastic instability due to external pressure and loads is not covered explicitly by the Section VIII Division 2 Rules. Nor are they covered by the B31 piping code rules. The user must recognize conditions where elastic instability can be a problem. Most common vessel and thin-walled piping geometries are not subject to elastic instability providing they are designed in accordance with the Code for external pressure. For large openings subject to heavy loads, and where diameter-to-thickness ratios exceed 100 and external pressure is a design criteria the designer is urged to exercise caution. The full version of FE/Pipe has several techniques available for evaluating elastic instability. 2) The ASME Section VIII Division 2 Code provides additional rules (See 4-136.7) for simplified elastic/plastic analyses. The rules of Section 4-136.7 allow the analyst to apply considerably larger secondary loads to nozzles without violating the Codes rules, its intent, or the Code desired safety factor against failure. This evaluation capability is typically NOT used in design. Should the user wish to take advantage of Code rules, which may permit extremely high secondary loads applied over a limited number of cycles, he should contact his software representative. 3) Occasional loads that may contribute to cyclic failures should be evaluated in terms of contribution to a cycle life fraction. Options are available to perform this type of evaluation if the need should exist; for example, the occasional loads are due to vibrations. The following gives a brief discussion of the calculated stresses and allowables.
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Primary (Sustained) Membrane Stresses: Primary Bending Stresses: Secondary Stresses: Peak (Fatigue, or Expansion) Stresses:
Pl < (1.5)(k)(Smh) Qb < (3.0)(Smh) Pl+Pb+Q < (3.0)(Smavg) < 2Sy Pl+Pb+Q+F < Sa < f (1.25(Sc+Sh) < (C) N-0.2
Pl
Local membrane stress due to weight and pressure – sustained, or primary loads.
k
Occasional load factor. 1.0 – weight and pressure, 1.2 – occasional.
Smh
Hot allowable stress
Pl+Pb+Q
Secondary stress on inner and outer fibers due to both the “range” of stresses and the sum of the primary and secondary stresses. (The range calculation insures elastic shakedown, and the sum of primary and secondary stresses insures that incremental straining per the Bree diagram will not occur.)
Smavg
The average of the material hot and cold allowables.
Sy
The material yield average yield strength.
Pl+Pb+Q+F
Peak stresses on the inner or outer fibers due to the “range” of stresses. This stress will cause a fatigue crack to occur.
Sa
Allowable from the ASME Section VIII Division 2, Appendix 5 allowable stress curve. Note that this value is computed based on an allowed number of operating load cycles. If not given this value defaults to 7000 cycles, a value selected by one of the original piping code developers, A.R.C. Markl, and used in most piping programs worldwide today.
f
Cyclic reduction factor based on the number of cycles. “f” usually starts at “1.0” for 7000 cycles. The empirical expression f = 6N-0.2 can be substituted for “f:”.
Sc
Piping Code – Cold allowable stress.
Sh
Piping Code – Hot allowable stress.
C
Constant used in Markl’s equation for allowable fatigue strength of materials. The value most commonly used for low carbon steels is 245,000 psi.
Typical “primary,” “secondary,” and “fatigue” stress reports are shown below. Highest Primary Stress Ratios Header at Junction Pl 2,651 psi
1.5(k)Smh 26,250 psi
Primary Membrane Load Case 1 Plot Reference: 1) Pl < 1.5(k)Smh (SUS,Membrane) Case 1
10% Branch at Junction Pl 12,969 psi
1.5(k)Smh 22,500 psi
Primary Membrane Load Case 1 Plot Reference: 1) Pl < 1.5(k)Smh (SUS,Membrane) Case 1
57% Highest Secondary Stress Ratios Header at Junction
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Pl+Pb+Q 6,427 psi
3(Smavg) 52,500 psi
Primary+Secondary (Outer) Load Case 2 Plot Reference: 4) Pl+Pb+Q < 3(Smavg) (OPE,Outside) Case 2
12% Branch at Junction Pl+Pb+Q 19,549 psi
3(Smavg) 45,000 psi
Primary+Secondary (Inner) Load Case 2 Plot Reference: 3) Pl+Pb+Q < 3(Smavg) (OPE,Inside) Case 2
43% Highest Fatigue Stress Ratios Header at Junction Pl+Pb+Q+F 4,338 psi
Sa 45,711 psi
Primary+Secondary+Peak (Outer) Load Case 2 Stress Concentration Factor = 1.350 Strain Concentration Factor = 1.000 Cycles Allowed for this Stress = 1000000.0 'B31' Fatigue Stress Allowable = 43750.0 Markl Fatigue Stress Allowable = 41701.0 Plot Reference: 6) Pl+Pb+Q+F < Sa (EXP,Outside) Case 2
Sa 42,854 psi
Primary+Secondary+Peak (Inner) Load Case 2 Stress Concentration Factor = 1.350 Strain Concentration Factor = 1.000 Cycles Allowed for this Stress = 614030.6 'B31' Fatigue Stress Allowable = 37500.0 Markl Fatigue Stress Allowable = 41701.0 Plot Reference: 5) Pl+Pb+Q+F < Sa (EXP,Inside) Case 2
9%
Branch at Junction Pl+Pb+Q+F 13,196 psi 30%
Each of the reported stresses corresponds with the individual items discussed above. Output is organized on a “region” basis. Two typical regions are shown, although usually there are more. Additional regions exist for thickened, or self-reinforcing nozzles, nozzles with repads, etc. In each case the stress for all regions in the model must satisfy the Codes requirements. Each reported stress has associated with it a “plot reference.” The “plot reference” can be used to review the distribution of the reported stress over the entire surface of the geometry. In general the stresses that are computed by a finite element calculation are very local. Only a small region of the model should show to be red, (or highly stressed). This is the desired stress condition. Very small, high stress regions plastically deform a small volume of material and redistribute their load to the relatively large elastic volume surrounding them. These types of “higher” localized stresses are safe and serve only as a potential site for a fatigue crack initiation. If a high, secondary stress is distributed broadly over the geometry then it becomes less “safe.” Large regions of red are, in general, significantly worse than small, local regions. The plots below illustrate.
Copyright (c) 2007 by Paulin Research Group
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Figure 1 – Broadly Distributed Stress Zones – The governing stress for the design is distributed over a significant part of the diameter, that is, greater than 50% of the total circumference.
Figure 2 – Local Stress Zones – The governing stress for the design is distributed over a fairly small part of the diameter, that is, much less than 50% of the total circumference. Structural output is grouped under longitudinal and circumferential plates, depending on the cross section selected. Each plate has a region described in the output as SCR. The stresses reported in this region are the plate stresses that are adjacent to a weld zone. SCR stands for Stress Concentration Region. SCR regions exist for plates along the outside edges of the plate that is adjacent to another construction.
Copyright (c) 2007 by Paulin Research Group
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Chapter 3 – Section 3 Pressure Design using 3d Shell Elements Pressure design of nozzle and structural connections near discontinuities in pressure vessels or piping usually involves satisfying the primary stress rules of the ASME Section VIII Division 2 Appendix 4 Code where the local membrane stress must be less than 1.5 times the hot allowable stress, and the local primary bending stress, when added to other secondary (Q) stresses must be less than three times the average of the hot and cold allowable stress. The ASME Code in Art 4-136 also provides for the use of plastic analysis to relax the rules outlined above, but these methods are not incorporated into FE/Pipe or NozzlePRO and do not see wide useage today although this is expected to change. The cyclic effect of pressure is included in the discussions in Appendix 4 and 5, and in particular in Art 4-6 in that cycling pressure definitely contributes to the Pl+Pb+Q+F alternating peak stress. Fatigue failures due to external loads in the accompaniment of pressure almost always occur at the toes of fillet welds. This peak stress is well evaluated in the FE/Pipe shell element model where the stiffness at the intersection is replicated and the stress at the fillet or radius toe is found in the first element in the parent shell or nozzle away from the penetration line. When pressure is the major contributor to a cyclic fatigue failure the peak stress often occurs at the inside corner of the geometry. This stress is not well described by a shell element model that stops at the fillet toes when the d/t ratio gets smaller. There are several ways to deal with this problem. 1) Calculate the stress at the penetration line and ignore any increase in strength due to fillets. 2) Calculate the stress at the penetration line and include the increase in strength due to fillets, (i.e. taper the elements.) 3) Adjust the SCF for this problem so that external loads are calculated conservatively, and the pressure stress is more suitably calculated. 4) Run brick models of the nozzle intersection to compare to the shell calculations to guarantee conservatism. Brick models do a good job of characterizing the peak compressive stresses on the inside corner of the thick nozzle geometry well. Version 4.0 of NozzlePRO lets the user do this brick comparison for nozzles in heads. Version 5.0 will extend this capability to cylinders. For the time being, only FE/Pipe users have access to this option. PRG is also doing geometry correlations with brick models in an attempt to develop a correlation for the corner stress increase due to pressure. An SCF of 1.6 has been used previously as per the suggestion in (3) above. A pressure stress only button exists on the Options data form that will zero all other loads and compute stresses at the penetration line. This is included for users wishing to experiment on their own with this effect to determine suitable SCFs. A portion of a primary stress ratio report is shown below: Highest Primary Stress Ratios Header at Junction Pl 2,651 psi
1.5(k)Smh 26,250 psi
Primary Membrane Load Case 1 Plot Reference: 1) Pl < 1.5(k)Smh (SUS,Membrane) Case 1
10% Branch at Junction Pl 12,969 psi
1.5(k)Smh 22,500 psi
Primary Membrane Load Case 1 Plot Reference: 1) Pl < 1.5(k)Smh (SUS,Membrane) Case 1
57%
Pl is the local primary membrane stress. The allowable for pressure design is 1.5 times the hot allowable stress. Satisfying these stress allowables for internal pressure tends to produce safety factors against burst in excess of 4.0, and in general will produce safety factors against burst of between 5.0 and 8.0. These results are from tests of intersections at room temperature. Note that as the Pl limit due to pressure approaches the allowable, the permissible external primary loads approach zero!
Copyright (c) 2007 by Paulin Research Group
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It is not uncommon for pressure failures to occur during hydrotest. ASME Section VIII Division 2 limits the general primary membrane and primary membrane plus bending stress intensity limits during test in AD-151.1: Pm < 90% Sy (at test temperature) Pm+Pb < 1.35 Sy for Pm < 0.67 Sy Pm+Pb < 2.15Sy – 1.2Pm for Pm > 0.67Sy and Pm <= 0.9Sy… (Sy at test temperature) Unfortunately, the Pm and Pb stresses are NOT the stresses found at discontinuities, for example, nozzles. The discontinuity stress components Pl and Q will clearly be higher than the general membrane stress intensities. Certainly, however, we may say that if we replace Pm with Pl, and Pm+Pb with Pl+Pb+Q in the above limits, and satisfy them, then the Code requirements for hydrotest are satisfied. The user may indeed make this comparison by hand. Unfortunately, the hydostatic test pressure may still be satisfactory if these conservative limits are not satisfied. Including pressure stiffening in FE/Pipe may reduce this conservatism some. A few tests have shown that a reduction in higher d/t intersections of about 10% can be expected due to pressure stiffening. When substituting Pm with Pl to check AD-151.1 the value of Pl must be calculated using the hydrotest pressure, not the design pressure! Problems generally occur in several recognized situations: 1) 2) 3) 4) 5) 6) 7)
Code Area Replacement rules are taken to the limit, i.e., area required = area available. The branch to vessel thickness ratio is approximately 1.0, i.e., t/T=1.0 The opening is a hillside or lateral connection. Pl > 72% of the allowable. (In the design case.) Calculated values for Pl or Qb are broad in extent. (See Figure 1 above.) Larger D/T openings and larger d/D openings. (D/T>80, and d/D>0.7) Weak blink flanges are suspected of being an accomplice, but no immediate test data is available.
The above does not imply that there will always be problems in these situations, but these are the general cases where hydrotest problems such as bursting or distortion have been observed. Full versions of FE/Pipe can read in the NozzlePRO input files and perform a simplified plastic analysis if necessary to assure that highly stressed areas are indeed local in nature, i.e. local plasticity redistributes loads to low stress regions.
Copyright (c) 2007 by Paulin Research Group
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Chapter 3 – Section 4 Stress Intensification Factors and Flexibilities A typical Stress Intensification Factor Report is given below: Computed Stress Intensification Factors Branch/Nozzle Sif Summary
Axial : Inplane : Outplane: Torsion : Pressure:
Peak 1.213 1.548 2.605 0.916 6.494
Primary 1.162 1.451 2.451 1.102 6.068
Secondary 1.798 1.812 2.896 1.357 9.250
The above stress intensification factors are to be used in a beam-type analysis of the piping system. Inplane, Outplane and Torsional sif's should be used with the matching branch pipe whose diameter and thickness is given below. The axial sif should be used to intensify the axial stress in the branch pipe calculated by F/A. The pressure sif should be used to intensify the nominal pressure stress in the PARENT or HEADER, calculated from PD/2t. Pipe OD : Pipe Thk: Z approx: Z exact :
24.000 8.000 1608.494 1340.412
B31.3 Peak Stress Sif ....
B31.1 Peak Stress Sif ....
WRC 330 Peak Stress Sif ....
in. in. cu.in. cu.in.
0.000 1.054 1.138 1.000
Axial Inplane Outplane Torsional
0.000 1.000 1.000 1.000
Axial Inplane Outplane Torsional
0.000 1.000 1.500 1.000
Axial Inplane Outplane Torsional
Notes: 1) For input into most pipe stress programs only the Inplane and Outplane Peak stress intensification factor can be used. (Markl testing done in the 50’s concentrated on only these loading directions.) Axial and pressure stress intensification factors are given for reference, and for the case where any of these loads cycle in a critical situation and the actual magnitude of the resulting stress should be estimated. (Most piping program users will have to make that evaluation by hand.) 2) Stress intensification factors (SIF’s) are paired with a section modulus! The piping program user should apply the SIF’s at the cross section whose OD and thickness match those given in the SIF reports above. 3) The values printed under the headings: B31.3, B31.1 and WRC 330 are given for reference. (WRC 330 was released as WRC 329.) 4) In cases where the nozzle thickness is significantly greater than the header or vessel thickness SIF’s can become quite large, often in excess of 20. Many piping engineers are not used to seeing SIF’s of this magnitude. The reason for this is that most piping programs print only the Code calculated “i” factor when generating reports, but then adjust it (according to the effective section modulus rules in the piping code) before making the stress calculation by the ratio of t/T, where “t” is the thickness of the branch and “T” is the thickness of the header. Clearly, where t >> T, the multiplication of “i” by t/T produces a significantly larger value for the actual stress intensification factor. The stress intensification factors given in the finite element reports shown above are already multiplied by t/T where applicable. Copyright (c) 2007 by Paulin Research Group
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5) When the calculated SIF, or “i” factor, is less than 1.0, the value of 1.0 should be used. In general, this means that the component is stronger in fatigue than a girth butt weld – but since the actual locations of girth butt welds are not specified in most fossil-petrochemical type pipe stress programs the Code user is penalized by being required to treat every pipe section as if it were a girth butt weld. 6) The approximate section modulus calculation given above is found from the expression (3.14)(r2)(t), where r is the mean radius of the pipe and t is the thickness. Stress Intensification Factors are generated typically for a vessel or large pipe connection and provided to a pipe stress engineer for use in a piping program. Pipe stress engineers are generally interested in these values since the B31.3 Code has published restrictive guidelines for use of the standard Code Stress Intensification Factors, eg:: “B31.3 Table D300 Note (1) Stress intensification and flexibility factor data .. are for use in the absence of more directly applicable data … their validity has been demonstrated for D/T <= 100. “B31.3 Table D300 Note (12) The out-of-plane stress intensification factor for a reducing branch connection with … 0.5 < d/D < 1.0 may be nonconservative. Selection of the appropriate SIF is the designer’s responsibility. A typical Flexibility Factor Report is given below. Flexibilities The following stiffnesses should be used in a piping, 'beam-type' analysis of the intersection. The stiffnesses should be inserted at the surface of the branch/header or nozzle/vessel junction. The general characteristics used for the branch pipe should be: Outside Diameter = Wall Thickness =
24.000 8.000
in. in.
Axial Transverse Stiffness Inplane Rotational Stiffness Outplane Rotational Stiffness
= = =
4107916. 23134282. 15084985.
lb./in. in.lb./deg in.lb./deg
The following stiffness(es) were not generated because of errors in input or because the finite element model is stiffer than the piping model. Torsional Rotational Stiffness
The factors given in this report are intended to be used as referenced in ASME Section III NB-3686.5. This Nuclear Code section instructs the user to insert a “Rigid Length” between the centerline of the header pipe or vessel and the surface of the header or vessel at the point where the nozzle penetrates. Point springs, having the stiffnesses given above, should be inserted at that point between two 6 degree-of-freedom piping nodes, one on the end of the rigid, and the other on the end of the branch or nozzle. Stiffnesses not calculated should be made rigid. This is generally the two shear, translational directions, that is, the user must add two additional rigid translational stiffnesses between the two nodes described above that are mutually perpendicular to the flexible axial direction of the nozzle. In the flexibility factor report given above, the Torsional Rotational Stiffness was found to be stiffer or the same in the finite element model as in the beam model of the intersection. When this is true, the beam model alone, without stiffnesses, should suffice, and the user should enter a rigid stiffness between the two nodes for the rigid degree of freedom. The finite element stiffnesses are generated automatically during the calculation by constructing a beam model of the intersection that includes the “Rigid Length” described above. The stiffnesses are computed such that the results from the finite element calculation match the results from the beam program when the stiffnesses are inserted into back into the beam model. There is no “rigid length” for head flexibilities. The point spring should be put at the surface of the nozzle to the head. The displacement and forces associated with each direction for a hillside nozzle are shown in the figure below Copyright (c) 2007 by Paulin Research Group
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Hillside Directions
Outplane Exaggerated Displacements (View from Top)
Inplane Exaggerated Displacement (Side View)
Inplane Exaggerated Displacement (Top View)
Axial Exaggerated Displacement (Top View)
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Recommended Beam Model to Include Hillside Stiffnesses
The RYY is the inplane direction, and the RZZ is the outplane rotational direction. The Outplane Stiffness would be inserted between nodes 15 and 20 in the RZZ direction, and the Inplane Stiffness would be inserted between nodes 15 and 20 in the RYY direction. Since an axial force on the nozzle tends to produce a radial displacement of the nozzle coupled with an RY rotation the axial stiffness is often omitted. If the user wishes to include it, then the axial stiffness computed from NozzlePRO can be inserted between 15 and 20 in the radial direction with all other translational stiffness directions rigid. (The radial direction being defined by the 10-to-15 axial element direction.) Rigid element constructions to produce the observed translational and rotational displacement coupling due to the axial force can be conceived. It is always interesting to compare finite element results to the industry standards that have been used successfully for years. For flexibilities, the most readily available documents have been WRC 297 and NB3685. The generalpurpose version of FE/Pipe provides both of these calculations for direct comparison with the finite element result. For a d/D intersection of 0.5 and d/t=D/T=50, the comparisons are shown below: Stiffness Direction: Inplane Rotational Outplane Rotational Axial
WRC 297 **RIGID** 224,800 3,069,000
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NB 3685 117,700,000 33,290,000 N/A
Finite Element 2,022,641 448,588 798,896
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Chapter 3 – Section 5 Allowable Loads A typical allowable load report is given below. Allowable Loads SECONDARY Load Type (Range): Axial Force Inplane Moment Outplane Moment Torsional Moment Pressure
(lb. ) (in. lb.) (in. lb.) (in. lb.) (psi )
Maximum Individual Occuring 398030. 5306513. 3358105. 2343568. 344.
Conservative Simultaneous Occuring 120631. 1137199. 719650. 710264. 111.
Realistic Simultaneous Occuring 180946. 2412363. 1526608. 1065396. 111.
(lb. ) (in. lb.) (in. lb.) (in. lb.) (psi )
Maximum Individual Occuring 618455. 5998639. 5458219. 2938301. 422.
Conservative Simultaneous Occuring 178300. 1222872. 1182725. 847110. 111.
Realistic Simultaneous Occuring 267450. 2594104. 2508939. 1270665. 111.
PRIMARY Load Type: Axial Force Inplane Moment Outplane Moment Torsional Moment Pressure
Notes: 1) Maximum Individual Occurring Loads are the maximum allowed values of the respective loads if all other load components are zero. For example, a primary (or sustained) axial force of 618,455 lb. will not overstress the above nozzle if all other loads and pressure are zero. 2) The Maximum Individual Occurring Primary Pressure can be taken as a finite element calculation of the MAWP for the nozzle. 3) The Conservative Allowable Simultaneous loads are the set of loads that can be applied simultaneously without overstressing the nozzle. Usually the Conservative Allowable Simultaneous Loads are used to compare against the results of a pipe stress program. The Sustained Loads on the nozzle or branch are compared against the PRIMARY allowables, and the Operating or Expansion Loads on the nozzle or branch are compared against the SECONDARY allowables. Occasional Loads plus Sustained Loads can be compared to the PRIMARY allowables times the occasional load multiplier for the Code of choice, for example (1.2) for ASME Section VIII Division 2, and (1.33) for B31.3, etc. It is expected that the simultaneous application of the Conservative Allowable Simultaneous Loads will produce stresses that are approximately 60- to 70% of the allowable. 4) The Realistic Allowable Simultaneous loads are the maximum loads that can be applied simultaneously. These loads are based on experience at Paulin Research and are expected to produce stresses that are closer to 100% of the allowable. Users wishing to use the “Realistic Allowables”, however, should do further investigation to assure that all Code limits are properly satisfied. 5) Secondary allowable loads are based on the principles of elastic shakedown, incremental ratcheting, and fatigue. The number of operating cycles may influence these allowables, if fatigue governs the allowable load value.
Copyright (c) 2007 by Paulin Research Group
3.5.1
NozzlePRO
www.paulin.com
Chapter 3 – Section 6 Discussion of Results (Recommended Ways to Use the Output) Output appears in the browser window as shown below. Any web browser can be used, but the program output has been checked most thoroughly on Microsoft’s Internet Explorer.
Figure 3 – Example Output The screen contains three major areas: 1) Tabular Result Area (On the left side of the screen.) 2) Plot Title Area (In the upper right.) 3) Plot Display Area (In the bottom right.) The design is intended to facilitate the Code Stress evaluation procedure – which involves primarily: 1) Validating that the stress patterns “make sense” – i.e., reviewing graphical plots of stress results. 2) Making sure that the Code stress limits are satisfied. 3) Evaluating the “extent” of the stress state, i.e., is a local stress really “local?” The tabular output also provides other useful information such as: 1) Allowable nozzle loads. 2) Nozzle Stress Intensification Factors (For use in a pipe stress program.) 3) Nozzle Flexibilities (Also for use in a pipe stress program.) The reports are designed to be printed from each “frame.” Click on the “File” menu and then “page setup.” Portrait mode is selected typically. Adjust the top and bottom margins as needed to get two plots per page. For most reports, the leftmost frame is printed to obtain a tabular form of the results, and the bottom-right frame is printed to obtain the corresponding graphical form of the results. When reviewing output it is recommended to first visually validate the model. This involves moving the mouse to the slide bar on the right side of the screen, (opposite the graphical plot), and pulling it down – slowly moving past Copyright (c) 2007 by Paulin Research Group
3.6.1
NozzlePRO
www.paulin.com
the stress and displacement images. Each image should be studied for consistency. Questions that should be asked are: 1) Does the model look reasonable? 2) Is the vessel or pipe orientation correct? If the orientation is not correct the loads probably aren’t either. 3) Do the stresses make sense? An engineer or designer has a good idea what a pattern of stresses should look like. A good stress plot for the model above is shown below:
Figure 4 – Reasonable Stress Patterns High stresses exist as would be expected in the sustained case around the knuckle of the dished head. In fact, these stresses are of the same magnitude as the stresses in the nozzle. We can see this by noticing red regions close to the nozzle on the “minus X” side and close to the pad on the “plus X” side. This is the stress pattern we would expect from “X” and “Z” direction bending moments. The sustained loads that produced the above stress state are shown below: FX 1057
FY -1323
FZ -2333
MX 230000
MY 9833
MZ 123400
Other characteristics of a “reasonable” stress plot are as follows: 1) The stresses should not seem to congregate around element boundaries. The stresses do not know where element boundaries are in a finite element model. They should not artificially collect at these locations. FE/Pipe does not average shell stresses. This makes it easier for the user to tell when the stress state is not a good one. If the stresses localize themselves artificially around element geometries then something is wrong. Examples of “bad” stress states are shown below:
Figure 5 – Errant Stress Patterns. 1.
In the left figure the stresses are clearly segregated inconsistently around element borders. (This tends to occur with extremely thick geometries.) In the right figure, the highest stress is shown to exist at the top of the
Copyright (c) 2007 by Paulin Research Group
3.6.2
NozzlePRO
2. 3. 4. 5.
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spherical head at a small modeling opening. In the left figure, the stresses will have a much greater error than normally expected. In the right figure, the errant stresses at the top of the head must be ignored. Stress distributions due to bending moments show the characteristic high stress values on either side of the bending axis. Stress distributions due to torsional moments show a uniform stress state in the nozzle. Pressure stresses are often highest on the inside and in the longitudinal plane. The exception is repads where the highest stress may be at the edge of the repad and in the circumferential plane. Stresses should be highest at the nozzle/shell junction. High stresses at boundary conditions, or artificial model entities (like the high stress at the hole shown above) should be ignored.
Whereas considerable effort has been expended to make sure that solutions are generated for every range of nozzle to vessel geometry, pad size, thickness and orientation, there will be problems where errant solutions are generated. In almost all cases errant solutions can be found by looking at the stress-state and applying common sense. If the stresses make sense then the solution is probably correct. If they do not, then there may be a problem, and the solution should not be used until the question is resolved. An example poorly generated mesh plot appears below. The result from this calculation clearly should not be used.
Figure 6 – Incorrect Element Mesh Layout Plots may show titles such as: 6) Pl+Pb+Q+F < Sa (SIF outside). Whenever a plot label is shown with the words SIF in the title, the plot has been generated only to show the distribution of stress due to a single load direction. There will be no stress legend, because the magnitude of the stress is unknown. Only the distribution of the stress is known. These plots are used typically to direct inspections or to validate that a particular failure was caused by an individual load. For example, an out-plane SIF plot is shown in the figure below:
Figure 7 – SIF Plot There is no stress legend shown because the magnitude of the stress is not known. From this plot the user knows only that an out-plane moment on this nozzle will produce a high stress in the nozzle neck just above the weld. Any inspection should concentrate on this area if the out-plane moments on the nozzle are known to be high.
Copyright (c) 2007 by Paulin Research Group
3.6.3
NozzlePRO
www.paulin.com
Chapter 4 – Section 1 When to Use NozzlePRO Saddles & Pipe Shoes Horizontal Vessels Typically, horizontal vessels are designed using the methods presented by L.P. Zick. Although widely used, Zick’s methods do not provide means for a full analysis including all expected loads, both internal and external. The following are several instances where Zick’s methods are not appropriate for analysis:
• • • • • •
Axial loads (Internal splashing, earthquake loads, wind loads, expansion) Transverse loads (Internal splashing, earthquake loads, wind loads) Cyclic loadings for fatigue analysis Wear plate geometries beyond the scope of Zick’s recommendations (b +10t, etc) Evaluation of stresses for non-integral wear plate geometries. Saddle support member stresses.
The most significant shortcoming of Zick’s methods is the lack of design methods for axial or transverse external saddle loads. Axial loads are becoming increasingly important as seismic codes increase the loadings and more vessels are built for offshore applications. Until now, there has not been a simple and direct tool for the evaluation of stresses in the vessel and saddle support caused by external loads. NozzlePRO eliminates the need to develop approximations for stresses caused by axial or transverse loads. These subjects have never been fully addressed due to the complexity of the interaction between the saddle and vessel. Most research and theoretical work has focused on the same problem addressed by Zick: stresses caused by dead loads and pressure. With only a few entries, NozzlePRO reduces a complex problem to a simple solution. From an engineering and design aspect, NozzlePRO will save time and money by eliminating the often confusing and inconsistent methods used to analyzed external loads on horizontal vessels. Instead of focusing on how to solve the problem of external loads, engineers can now spend time optimizing designs while gaining greater confidence in the end results. The basic concept behind the NozzlePRO saddle models is that the engineer can fully capture all load conditions while only using one-half of the symmetric vessel in the analysis. The user should include self-weight, liquid head, and external loads applied to the saddle base plate. In addition, it is important to always check the hydraulic case (full of liquid, no internal pressure) since this will usually result in the greatest stresses. In general, NozzlePRO results for primary plus secondary stresses (Pl+Pb+Q) will correlate best with Zick’s predictions for circumferential bending stress at the horn of the saddles. For most cases, NozzlePRO results will likely predict more conservative stresses than give by Zick. A discussion on the reasons is presented later. At PRG, we are currently implementing several new features and conducting full scale testing to verify the models produced in NozzlePRO. Look for features such as bearing stresses in non-integral wear plates, internal and external stiffening rings, and full encirclement saddles in upcoming releases.
Pipe Shoes Pipe shoes are routinely designed using simplified methods and approximations such as line loads, distributed bending loads, and various WRC type calculations. However, with NozzlePRO no approximations or assumptions are necessary any longer. Nearly any geometry can be easily analyzed. NozzlePRO should be used for pipe shoe analyses when: • • • • •
High reaction loads are acting upon pipe shoe and piping. Cyclic loading at the pipe shoe is evident. Axial loads present with restrained base plate. To evaluate flexibility of pipe shoe for reduced piping stresses. Large D/t piping where full encirclement saddles are not applied.
Copyright (c) 2007 by Paulin Research Group
4.1.1
NozzlePRO
www.paulin.com
Chapter 4 – Section 2 Saddle and Pipe Shoe Input Screens and Saddle Wizard An example saddle model is shown below. To begin a model, just select the base shell type “CYLINDER” and the Nozzle/Attachment Type “SADDLE” or “PIPE SHOE”. For the cylinder, the only required entries are outside diameter and wall thickness. However, for horizontal vessels it is recommended that one-half the vessel length is specified. The remaining entries for saddle dimensions are shown below. Note that the wear plate is optional and not required to perform an analysis. Other entries such as loads and materials follow the same format and methodology as for nozzles and other attachments. Building pipe shoes requires nearly the same procedure as for saddles.
Once the general geometry has been established, use the Saddle / Shoe Options screen for additional control over the support design and loading options. The following are a few general suggestions that have been shown to provide good results: • • • • • • • •
For horizontal vessels, use one half the tangent length for the cylinder and Symmetric load option For pipe shoes, use default NozzlePRO length and loads applied to saddle, far-end and near-end fixed load option. Deactivate elemental smoothing in the OPTIONS screen. Apply axial or transverse loads only to the saddle or pipe shoe base plate, not to far-end of model Evaluate axial loads in both directions to see interaction with other loads (dead load, pressure) Include self-weight and liquid weight when these are a significant factor Do not apply a crude mesh multiplier for non-integral wear plates If internal liquid is part of load case, do not include pressure since it will reduce stresses at saddle horn by minimizing the circumferential bending.
Copyright (c) 2007 by Paulin Research Group
4.2.1
NozzlePRO
www.paulin.com
Saddle / Shoe Options Form Most of the saddle and pipe shoe modifications will be performed through the Saddle/Shoe options screen shown below. These options are available by clicking “OPTIONS” in the main screen, and then clicking “Saddle / Shoe Options” located in the lower right corner.
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4.2.2
NozzlePRO
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MODEL OPTIONS
Use Non-Integral Wear Pad When a wear plate is specified in the main screen, the default model is an integral wear pad. An integral wear pad model simply increases the thickness of the shell elements within the region of the wear pad. Here, the total thickness will be the specified vessel wall thickness plus the wear plate thickness. However, the mean radius of the vessel will remain unchanged. A non-integral wear pad model creates a separate surface that represents the individual geometry of the wear pad. The non-integral wear pad is joined to the parent shell along the free edges of the wear pad. Thus, forces are only transmitted through the edges of the wear pad. With the non-integral wear pad it is assumed that the wear pad and vessel are not in contact except along the perimeter of the wear pad. All webs plates are attached to the wear plate only; they are not attached to the vessel shell. Currently, it is assumed that the non-integral wear plate and vessel do not bear against one another. However, work is currently underway at PRG to implement bearing stresses between the non-integral wear plates and vessel. When using the non-integral wear pad model, the global mesh multiplier should usually not be less than 1.0. A global mesh multiplier less than 1.0 will likely cause the small weld elements that connect the wear pad to the vessel to collapse. These collapsed elements will cause the analysis to abort and report an error. In some instances, very thin non-integral wear pads used in large diameter vessels might result in numerical instabilities in the stiffness matrix. Such a condition is caused by the small numeric coefficients of the weld elements in relation to the large numeric coefficients of the overall geometry. See the Integral and Non-Integral Wear Plate Comparison section for a more detailed discussion of the wear plate options.
Copyright (c) 2007 by Paulin Research Group
4.2.3
NozzlePRO
www.paulin.com
Elements along Saddle/Shoe Height This optional entry allows the user to specify the number of elements along the vertical edge of the web plates. The default value is typically sufficient. Fix Rotations of Saddle Base Plate The default is for fixed longitudinal rotation of the base plate. Alternatively, the user may wish to allow rotation to evaluate the effects. Material Density Used on only when the self-weight of the horizontal vessel or pipe is to be included in the analysis. This should only be used when using the Symmetric load option to model one-half of an axisymmetric vessel or pipe. Units are (lb/in3) and (kg/m3). Liquid Height from Bottom of Vessel Used only when the liquid head is to included in the analysis of a horizontal vessel or pipe. This entry should only be used when modeling one-half of an axisymmetric vessel or pipe. Specific Gravity When a liquid height is specified, the specific gravity must also be included. Enter the specific gravity of the liquid in this text box.
Include Material and Fluid Weight If self-weight and liquid weight is to be included in the analysis, this option must be marked. This option should be used if the recommended Symmetric load option is to be used. Gravity Multiplier This option allows the user to input various gravity loads in the global X, Y, and Z coordinate directions. Instances where GX and GZ might be applied is for the evaluation of seismic or ocean transport.
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4.2.4
NozzlePRO
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SADDLE OPTIONS
Circumferential Flange Plate Location Used to specify the location of the circumferential web plate in the saddle support. Options include placing a flange plate at the front, back, middle, front and middle, and back and middle.
Distance from front boundary condition to support centerline. Specifies the distance from the front end of the model to the centerline of the support. This is comparable to the dimension “A” in Zick’s analysis for horizontal vessels. As recommended in most references, this value should not exceed one quarter of the vessel’s tangent length.
Copyright (c) 2007 by Paulin Research Group
4.2.5
NozzlePRO
www.paulin.com
Width of saddle at base plate This option is used indicate the transverse width of the saddle at the base plate.
Circumferential plate thickness If the circumferential plate is a different thickness than the web plates, then the user may enter the appropriate value in this field.
Axial length of saddle at base plate This entry provides the user the ability to designate a tapered saddle design as shown below.
Axial base plate location The axial base plate location options allow the user to designate the direction of the axially tapered saddle. This option can be used to taper the saddle towards the head (Front of Saddle), the midspan (Back of Saddle), or a symmetric taper about the support centerline (Middle of Saddle). The figure above would be created by selecting “Back of Saddle”.
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4.2.6
NozzlePRO
www.paulin.com
SHOE OPTIONS
Distance from Front Boundary Condition to Support Centerline (Pipe Shoe Option) Specify the distance from the front end of the model to the centerline of the support. For pipe shoes located in a continuous run of pipe, it is best to locate the pipe shoe in the center of the geometry.
Width of Shoe at Base Plate This option is used to specify the transverse width of the shoe near the base plate. Transversely tapered pipe shoes can be generated using this option.
Number of Longitudinal Plates An optional entry that allows the user to specify the number of longitudinal plates contained in the pipe shoe. See the figure below for details.
End Plate Location Selecting one or more of the options allows transverse end plates to be placed at the front side, back side, or middle of the pipe shoe. See the figure above for details.
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4.2.7
NozzlePRO
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LOAD OPTIONS
Load Options Five various load conditions are provided. When horizontal vessels are to be analyzed, the Symmetric load option is the recommended (and default) load option. However, the Symmetric load option will require modeling half of a symmetric horizontal vessel. The remaining four load options should only be used for pipe shoe models, not horizontal pressure vessels. Symmetric Far-End, Axial Forces on Saddle, Weight and Pressure – Recommended for Horizontal Vessels Most often, horizontal vessels are symmetric about their midspan. When modeling a symmetric horizontal vessel, this load option is the recommended selection. The resulting model should produce identical stresses and deflections in comparison to a full model of the horizontal vessel. The advantage is the significantly reduced computation time.
IMPORTANT For axisymmetric modeling, the cylinder length must be one-half the tangent length of the vessel. Self-weight, any liquid head, and pressure must also be included.
Since the model is to intended represent a vessel with symmetry about the midspan, self-weight and any liquid head must be included in the model. If axial saddle loads are present, these should be entered into the Loads screen, accessible through the main NozzlePRO screen. To allow deflection and ovaling of the shell, a SYMFIX boundary condition is applied at the midspan. The SYMFIX boundary condition fixes only axial translation and local in-plane rotation of the shell. In addition, the saddle is modeled as a guided sliding saddle with only X-direction translation free. By default, rotations of the base plate are also fixed. However, rotations may be freed using the appropriate option switch located in the Saddle / Shoe Options screen.
Forces on Saddle/Shoe – Front End and Far End fixed. This is the recommended load option for pipe shoe analysis. It readily approximates the conditions for a continuous run of pipe with internal pressure. For saddle supported vessels, this option would only be used if the saddles are located far enough from a head support to ensure no interaction between the head and saddle region. Since such a condition does not routinely exist, it is not recommended to use this load option for saddle supported vessels. This loading option applies the specified forces to the base plate of the saddle/shoe. Loads should be specified in the Nozzle Loads screen, accessible through the main NozzlePRO screen. The front end (near end) is fixed against transverse and rotational movement, but free for axial translations. The front is end typically referred to as PFIX in FE/PIPE since it allows the model to generate PD/4t stresses. The back end is fixed against all translations and rotations. Copyright (c) 2007 by Paulin Research Group
4.2.8
NozzlePRO
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Forces on Saddle/Shoe – Front End Head, Far End Fixed. With this option, loads are applied to the base plate of the saddle or shoe. Loads should be applied using the Nozzle Loads screen available through the main NozzlePRO interface. Options for heads at the front end include elliptical, hemispherical, and flat heads. The far end is fully fixed for all degrees of freedom.
Forces on Far End - Saddle/Shoe Fixed, Front End Head Forces are applied to the far end of the vessel through a rigid end cap. In addition, the far end is free for translational displacements, but fixed against any rotations. The saddle is fixed against all rotations and translations. However, saddle rotations may be allowed through the “Fix Rotations of Saddle Base Plate” option. At the front end, the user’s choice of head is created.
Forces on Far End - Saddle/Shoe Fixed, Front End Fixed For this load option, forces are applied to the far end of the model through a rigid end cap. Here, translations are allowed, but rotation is fixed. The saddle or pipe shoe base plate is fixed against translation and rotation unless rotations are freed with the “Fix Rotations of Saddle Base Plate” option. A PFIX boundary condition is applied to the front end of the model. PFIX fixes all rotations and translations except for axial movement. PFIX also allows the PD/4t pressure loads to be developed in the model.
FRONT HEAD OPTIONS
Front End Head Type Here, the user picks which type of head will be applied to the front end of the model. This only applies for Load Options that implement heads at the front-end of the model. Head Thickness This option allows for cases where the head thickness is different than the cylinder thickness. If no entry is made, the default thickness is automatically taken as follows: • • •
Spherical = 1/2 x Cylinder Thickness, Elliptical = Cylinder Thickness, Flat = 6 x Cylinder Thickness.
Copyright (c) 2007 by Paulin Research Group
4.2.9
NozzlePRO
www.paulin.com
Saddle Wizard When Selecting the Saddle Option in the Nozzle/ Attachment Type section you will be asked if you want to use the saddle wizard to build your model. Select Yes to begin the wizard.
Axial Taper There are four different types of axial taper’s to choose from. Select the desired Axial Taper and click on NEXT.
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4.2.10
NozzlePRO
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Transverse Taper There are three different types of Transverse Taper’s to choose from. Select the desired Transverse Taper and click on NEXT.
General Dimensions Enter the dimensions and click on NEXT.
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4.2.11
NozzlePRO
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Saddle Dimensions Enter the saddle dimensions and click on NEXT.
Wear Plate If using a wear plate select “Yes” and there is also an option of using a Non-Integral Wear Plate. Enter the dimensions and click on NEXT.
Copyright (c) 2007 by Paulin Research Group
4.2.12
NozzlePRO
www.paulin.com
Gusset Plates Chose the number of Gussets and enter the thickness and click on NEXT.
Web Plate Data There are four options for the Circumferential Web Plates. Select and option and enter the Thickness and click on NEXT.
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4.2.13
NozzlePRO
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Internal Loads Enter the Internal Loads and click on NEXT.
Copyright (c) 2007 by Paulin Research Group
4.2.14
NozzlePRO
www.paulin.com
Analysis Type There are three options for the analysis type, each with a description in the widow below the options. If option 1 is chosen the wizard will skip the External Loads section. If options 2 or 3 are chosen the External Loads section will not be skipped. The user should refer to the descriptions provided for each option when deciding how to proceed. Choose the option and click on NEXT NOTE – Option #2 is not typically recommended for the analysis of saddle supported geometries subjected to external loads or accelerations. The reason is that only one-half of the vessel will be created with a rigid boundary condition at the mid-span which will restrict ovalization. This restriction will inhibit the actual deformation which a saddle supported geometry will experience during operation, leading to inaccurate solutions. The user should use Option #3 if external loads are present or Option #1 if no external loads are to be included.
External Loads - Option 2 If option 2 was chosen then enter the external loads described below and click on NEXT.
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4.2.15
NozzlePRO
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External Loads - Option 3 If option 3 is chosen then enter the external loads described below and click on NEXT.
Materials Enter the Material for the Vessel. If the Saddle Material is different than the Vessel Material deselect the “Saddle Material same as Vessel Material” option and enter the Saddle Material and click on NEXT.
Copyright (c) 2007 by Paulin Research Group
4.2.16
NozzlePRO
www.paulin.com
After completing the saddle wizard there will be four options. Select the option to finish with the wizard.
Copyright (c) 2007 by Paulin Research Group
4.2.17
NozzlePRO
www.paulin.com
Chapter 4 – Section 3 Applications of the Saddle / Shoe Modeler The saddle and shoe options have been provided to allow fast and efficient modeling of a wide range of support configurations. In most instances, the stresses around the saddle horn or pipe shoe are the primary concern. To ensure consistent results when modeling, the following sections provide some guidance and suggested methods.
Suggested Modeling Method for Horizontal Vessels When horizontal vessels are symmetric about their midspan, the recommended method for modeling is to use the Symmetric load option. The Symmetric load option allows the user to create an axisymmetric model of the horizontal vessel. By axisymmetric, it is meant that one-half of the full length vessel should be modeled. At the midspan, NozzlePRO uses a SYMFIX boundary condition that will allow for ovaling and deflection equivalent to that found in a full model. Other load options will not allow for ovaling at the midspan and will provide inconsistent results. The influence of ovaling and symmetric modeling can be seen in the following figures.
One-half Vessel Modeled with Load Applied at Far End. Notice there is no ovaling at midspan.
Full Vessel Modeled with Self-weight and Filled with Water. (FE/PIPE Required)
Copyright (c) 2007 by Paulin Research Group
4.3.1
NozzlePRO
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Symmetric Vessel Load Option Using NozzlePRO Self-weight and full of water.
The important point to note from the displaced figures is that the load options other than the SYMMETRIC load option do not allow for dilation, or ovaling, of the vessel at the midspan boundary condition. As can be seen in the upper displaced model view, the midspan remains circular. In comparison, the middle figure shows that the cross section does not remain circular when the entire vessel is modeled full of liquid using FE/PIPE. The last figure shows was generated using the Symmetric load option and produced the same deflected shape and stresses. Ovaling at the midspan of horizontal vessels is a significant characteristic of large L/D*t vessels. Notice that in the first figure, the midspan boundary conditions hold the section circular and push the ovaling further towards the saddle. As the ovaling nears the saddle, the increased rotations and displacements will tend to produce more conservative results. It is not recommended to allow NozzlePRO to calculate the default length for horizontal vessels. The default length will provide varying results depending on the type of load options used. When modeling less than half of a symmetric vessel, the results will vary dependent upon the length, diameter, and thickness of the vessel. When using less than one-half the tangent length , the results for horizontal vessel full of liquid become increasingly conservative as the vessel ratio L/D*t increases. High values of L/D*t represent long, thin walled, large diameter vessels. For these configurations the load options used in NozzlePRO will tend to produce deflections around the saddle horn in excess of those found in the full model. However, lower ratios of L/D*t have been shown to produce lower stresses than those found in symmetric models.
Suggested Modeling Method for Pipe Shoes Pipes supported on pipe shoes will show similar behavior as described above for horizontal vessels. While horizontal vessels should only use the SYMMETRIC load option, pipes may be evaluated using any of the load options. The results will vary slightly depending on the load option used. For example, applying loads to the FarEnd might not have the same effect as applying the loads to the pipe shoe. The user must evaluate the various load options, stress fields, and deformed shapes to determine the best load option for their particular piping arrangement. The best approach is to try and model the pipe and pipe shoe just as it will behave in the real world. Significant distributed loads should be modeled as such. If the base plate is fixed or has sliding friction, then model the external loads at the base plate. Also, boundary conditions should be representative of the actual model. Guided and sliding saddles should be modeled with the appropriate boundary conditions to simulate the same behavior. Large D/t piping supported on pipe shoes could likely see the same ovaling shapes as shown for horizontal vessels. In these cases, the user may elect to use the FE/PIPE editor to place a SYMFIX boundary conditions on both ends of the piping to allow ovalization on each side of the pipe support. However, the entire model will be locked against axial translations when using two SYMFIX boundary conditions since SYMFIX does not permit axial translation.
Copyright (c) 2007 by Paulin Research Group
4.3.2
NozzlePRO
www.paulin.com
Liquid Loads and Internal Pressure Typically, the hydraulic case (liquid only, no pressure) will cause the greatest stresses at the horn of the saddle. Circumferential stresses are greatest when the hydraulic case is taken with the vessel fully filled with liquid. The liquid head will cause the shell to “slump” over the horn of the saddle. However, when internal pressure is included, the bending will tend to straighten out and the saddle horn stresses will be reduced. Of course this will not be true for cases where the pressure stress alone is greater than the hydraulic stress. Considering these facts, the hydraulic case (no pressure) should always be analyzed. Since most horizontal vessels will be hydro-tested after fabrication, the full hydraulic case can not be disregarded. Often, hydrotest liquid loads can be significantly greater than the operating loads. For example, a horizontal vessel designed for gas only might be highly stresses during hydrotest if the liquid loads are not considered in advance.
Axial Loads Many horizontal vessels are subject to sloshing loads or axial loads caused by a variety of sources. Most governing design codes, including ASME and a host of seismic codes require the designer to consider the effects of all potential loads including those produced by seismic activity. Thus, any horizontal vessel located in a seismic zone should be analyzed for potential sloshing loads caused by seismic activity. In off-shore applications, horizontal vessels are continuously exposed to sloshing loads. These repetitive sloshing loads require the designer to consider the fatigue life of the vessel. While certain assumptions and closed-form solutions can be developed, NozzlePRO offers direct evaluation of any directional load acting on a horizontal vessel. SPLASH, a 2D free surface CFD modeler available from PRG, can quickly calculate the realistic sloshing loads acting on horizontal vessels. Assuming the full weight of the internal liquid is accelerated all at once is a simple assumption sometimes made. However, this can lead to very conservative designs, especially when fatigue life is a concern. Two cases should be run, one with the axial load in positive X-direction and one for axial load in negative Xdirection. When loaded by self-weight and liquid loads, the saddle will have the highest circumferential bending stress concentrated to one side of the saddle horn. Thus, the axial load will either increase the stresses at the saddle horn or decrease the stress depending if the axial load is working with or against self-weight and liquid weight.
Copyright (c) 2007 by Paulin Research Group
4.3.3
NozzlePRO
www.paulin.com
From the stress plot above, it is clear that the saddle stiffeners must be designed to accommodate the high bending stresses caused by the axial loads. In addition, this plot shows that the stresses around the saddle horn remain the highest in the vessel wall. Evaluation of several horizontal vessels subject to axial load has shown that the stresses near the bottom of the vessel will not govern, Depending on the design details, wear plates might either increase or decrease the stresses in the vessel shell. The behavior of wear plates under the influence of axial loads has been found to be similar as to the behavior of repads on nozzles. When the wear pad is thick in relation to the shell, the stiff wear plate causes the load to concentrate in the vessel wall, near the edge of the wear pad. Very thin wear plates provide only a small reduction of the axial load stresses. To a certain limit, a wider wear pad will also help reduce the effects of axial loads. However, Zick’s minimum width of (b+10t) is a reasonable starting point.
Copyright (c) 2007 by Paulin Research Group
4.3.4
NozzlePRO
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Chapter 4 – Section 4 Interpreting the Results Typical Stress Fields The use of the saddle models will require some understanding of the stress patterns in horizontal vessels, particularly near the support saddle. When viewing the graphical results, it is not readily apparent which stress regions are compressive and which are tensile. For example, both the highest compressive stress and tensile stress typically occur near the horn of the saddle. Knowing which stress intensities are compressive or tensile and where they should occur is important for determining allowable stress limits and proper fatigue stress (Pl+Pb+Q+F). At the horn of the saddle, the outer surface is usually in compression while the inner surface is in tension. To take the highest stress (typically compressive stress on outer surface) and use it for a fatigue analysis would not be the appropriate procedure. Instead, the proper stress would be that at the interior surface. Further above the saddle horn, near the meridian, the bending moment will usually reverse. Near the meridian, the outer surface will be in tension while the inner surface is in compression. In addition, the highest stresses will tend to gather on the edge of the saddle nearest to the midspan (inside edge). These stress field trends are illustrated below.
Tensile stress on outer surface near meridian
Compressive stress on outer surface at saddle horn
Stresses concentrate on inside edge of saddle
Pl+Pb+Q Stresses on Outside Surface
Users must be cautious when making comparisons to results from semi-empirical methods such as those presented by L.P. Zick. The stresses calculated in Zick’s method can not be directly compared to any of those generated by NozzlePRO. The reason is that Zick only reports stresses in longitudinal or circumferential directions (excluding transverse shear at saddles), and does not report both at any location. At the saddle horn, Zick only reports circumferential stresses whereas NozzlePRO will report the maximum stress intensity. After analyzing various horizontal vessels using NozzlePRO, PRG has found that Zick’s approximations for circumferential bending stresses at the horn of the saddle are closest to Pl+Pb+Q type stresses in this region. On the outside surface, both longitudinal and circumferential stresses will usually be of the same sign (compressive stress) when liquid loads without pressure are analyzed, with circumferential stresses dominating. Since the normal Copyright (c) 2007 by Paulin Research Group
4.4.1
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principal stress is typically near zero, the stress intensity near the saddle horn is highly dependent upon the magnitude of the circumferential stress. Thus, the reported stress intensity for Pl+Pb+Q stress should be slightly higher than the circumferential component alone provided that significant shear stresses are not present. FE/PIPE users can evaluate the local stresses in the circumferential and longitudinal directions using MODGEN commands. Typical stress fields for longitudinal and circumferential stresses are shown below.
Longitudinal Stress on Outside Surface
Circumferential Stress on Outside Surface
In most circumstances it has been found that the NozzlePRO results will be conservative in comparison to Zick’s methods when using the Symmetric load option. The variances in the results are likely explained by some of the inherent conditions of Zick’s analysis. One fact of the strain gauge testing is that the exact location of Zick’s strain gauges during the testing is unknown. This is important since the stresses decrease rapidly as one moves away from the saddle horn, towards the meridian. In other words, small changes in location can cause large changes in stress values. It is unlikely that Zick located the stain gauges directly next to the weld at the saddle horn or wear pad edge. Even if this were the case, the size of the strain gauges could have influenced the results in such a rapidly changing stress field. Thus, it is difficult to say Zick captured the absolute maximum circumferential bending stresses near the horn of the saddle. If wear plates are included in the model, Zick’s results could be even further from the NozzlePRO results since the stress field is highly dependent on the geometry of the wear pad (thickness, width, angle, etc). Even though Zick attempted to cover a range of geometries, it is possible that Zick’s experimental data never included the maximum stresses when wear pads were involved. As the figures show earlier indicate, the high stresses might occur behind the wear pad, locations inaccessible to strain gauges. This is particularly prevalent in vessels with wear pads less than the thickness of the vessel. Strain gauge testing, cyclic testing, and other testing of horizontal vessels in planned at PRG in the near future. How users address axially loaded horizontal vessel on saddle supports is of special interest. Those with questions, comments, or suggestions regarding the study of horizontal vessel supports are encouraged to contact PRG at [email protected]
Copyright (c) 2007 by Paulin Research Group
4.4.2
NozzlePRO
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Merge Regions Method The Merge Regions Method is an option available through the FE/PIPE editor that allows users to determine the means of calculating the stresses at plate line penetrations. NozzlePRO uses the default (and recommended) Merge Regions Option “1”. This sets the stresses at the junction of the plate and shell equal to zero then uses the stresses at the edge of the first element away from the junction to provide an average stress near the plate penetration. Alternatively, the user might wish to calculate the stresses in the shell directly at the plate line penetration. To report the stresses directly at the plate / shell intersection, the Merge Regions Method “0” should be used. The results are shown below.
Merge Regions Method “0”
Merge Regions Method “1”
Merge Regions Method “0” will tend to give more conservative stresses since the maximum stress will occur at the junction of the shell and plate. However, the stresses at this junction have been shown to be dependent upon the density of the mesh. This often occurs at sharp transitions or intersections in plate and shell models and is due to the singularities that occur at the nodes within the junction between shell and plates. Merge Regions Method “1” helps reduce the influence of the singularities. Using Merge Regions Method “1” and the default model mesh density will produce the most realistic stresses for horizontal vessels.
Copyright (c) 2007 by Paulin Research Group
4.4.3
NozzlePRO
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Chapter 4 – Section 5 Integral vs. Non-Integral Wear Plates The non-integral wear pad option has been included to allow users to evaluate the interaction of the wear plate with the parent shell. Engineering judgment must be applied when comparing results from non-integral and integral wear pad models. The recommended approach is to run both cases and evaluate the results. Since the non-integral model does not yet include radial bearing loads, the most accurate result will be some where between the nonintegral and integral cases. Zick’s results as well as other indicate the wear pad should move the high stress in the vessel shell away from the horn of the saddle, towards the meridian. In general, when t/T (wear pad thickness / vessel wall thickness) is less than 1, the highest stresses in the shell are likely to occur at some point between the saddle horn and the top of the wear pad. As the ratio t/T increases, the local bending stresses will move further away from the saddle horn and eventually will be the highest just outside the edge of the wear plate. Such a trend might not be apparent when using the integral wear pad model. Provided the loads are high enough to generate a noticeable stress field, the integral wear pad model should display this characteristic. The figures on the following page show how the thickness of the wear pad influences the stresses in the shell. Both non-integral and integral pad results are provided for comparison. Note that these figures were generated using Merge Regions Method “0”. A few conclusions can be made based on the plots below. First, both the integral and non-integral methods produce a reduction of the maximum stress found in the model without a repad. Integral pad models tend to produce similar trends and qualitative stresses in comparison to those predicted by Zick’s methods. However, the integral pad and Zick’s methods do not take into account the flexibility of the wear pad and the subsequent reduction of the stresses in the vessels wall. The non-integral pad models shown below illustrate the flexibility of thinner wear pads and the resulting reduction of stresses in the vessel wall. A balance exists for choosing an appropriate wear plate thickness. If the wear plate is too thin, the vessel shell stresses may drop, but the wear plate will see higher stresses. Note that both of the methods (non-integral and integral) show that thick wear plates will essentially move the peak stress to the edge of the wear and produce the highest stresses for cases where wear plates are used. For this reason, thick wear plates should be avoided. Note that only weight loads were included, not axial loads were applied to generate these plots. Thus, any conclusions from these plots may not hold for axial loads. As discussed previously, non-integral wear plates near the same thickness as the shell have shown to provide the best results for axial load induced stresses.
No Wear Plate (Pl+Pb+Q = 22,646 psi at saddle horn) (Zick = 16,038 psi) Copyright (c) 2007 by Paulin Research Group
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Non-Integral Pad Model Wear Plate Thickness = 0.375 x Shell Thickness (Pl+Pb+Q = 5,350 psi in shell, behind pad) (Zick = 13,547 psi at Horn & 12,197 psi at Pad Edge)
Non-Integral Pad Model Wear Plate Thickness = 0.50 xShell Thickness (Pl+Pb+Q = 6,600 psi in shell, behind pad) (Zick = 12,314 psi at Horn & 12,197 psi at Pad Edge)
Non-Integral Pad Model Wear Plate Thickness = 1.0 x Shell Thickness (Pl+Pb+Q = 8,900 psi in shell, at pad edge) (Zick = 7,705 psi at Horn & 12,197 psi at Pad Edge)
Copyright (c) 2007 by Paulin Research Group
Integral Pad Model Wear Plate Thickness = 0.375 x Shell Thickness (Pl+Pb+Q = 18,223 psi in pad area) (Zick = 13,547 psi at Horn & 12,197 psi at Pad Edge)
Integral Pad Model Wear Plate Thickness = 0.50 x Shell Thickness (Pl+Pb+Q = 16,257 psi in pad area) (Zick = 12,314 psi at Horn & 12,197 psi at Pad Edge)
Integral Pad Model Wear Plate Thickness = 1.0 x Shell Thickness (Pl+Pb+Q = 10,840 psi in pad area) (Zick = 7,705 psi at Horn & 12,197 psi at Pad Edge)
4.5.2
NozzlePRO
Non-Integral Pad Model Wear Plate Thickness = 1.5 x Shell Thickness (Pl+Pb+Q = 11,750 psi in shell, above pad) (Zick = 4,974 psi at Horn & 12,197 psi at Pad Edge)
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Integral Pad Model Wear Plate Thickness = 1.5 x Shell Thickness (Pl+Pb+Q = 11,360 psi above pad) (Zick = 4,794 psi at Horn & 12,197 psi at Pad Ed )
4.5.3
NozzlePRO
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Chapter 4 – Section 6 Other Topics Creating full models of horizontal vessels Entire models of vessels can be quickly created with a few commands using FE/PIPE. Note that the procedure described below requires the user to have full access to FE/PIPE in addition to NozzlePRO. The basic procedure is outlined below: 1.
2. 3. 4. 5.
6. 7.
Create NozzlePRO model and specify that the FE/PIPE files should be left in place. Note that it is not necessary to run the full analysis. All that is required is to plot the geometry since this will initialize the FE/PIPE input file. Locate the Nozzle.ifu file for the geometry that was created. In Windows Explorer, copy this file and rename (for this example “copy.ifu”). For copy.ifu, specify a negative X-axis orientation in the General screen. This spins the model around so that Nozzle.ifu and copy.ifu can be joined at their midspan. For copy.ifu and nozzle.ifu, change the “bottom” shell boundary conditions (at midspan) in FE/PIPE to include a node number for the data base operations. Any other boundary conditions at the midspan should be removed. Prepare nozzle.ifu and copy.ifu for analysis. Create a “none” type model and join nozzle.ifu and copy.ifu using the database operations.
For sliding saddles, or other boundary conditions, the input files must be modified accordingly.
Convergence of Stresses at Saddle Horn In any finite element model, the user must ensure that the stresses have converged. Convergence becomes especially important around plate/shell junctions. Plate and shell junctions are particularly susceptible to singularities. In other words, stresses that increase in some relation to increased mesh density. When refining the mesh in the default models there is a good chance that a singularity exists if the maximum stress continuously increases with increasing mesh density,. Under these circumstances, the user must evaluate the stress distribution and determine the most realistic stress removed from the singularity. Where the saddle joins to the vessel shell at the saddle horn, the maximum stresses are likely to be influenced by singularities. However, PRG has provided several features to reduce the effects of the singularities. Default model meshes and options will provide results that are conservative, but not unrealistic. Users wishing to evaluate the maximum stresses at the junction should refer to the section that discusses the Merge Regions Methods.
Large Models and Memory Allotment Horizontal vessel models will require more memory and take longer to analyze than other NozzlePRO models due to the higher number of shell elements. The memory requirements and computational time will be the greatest when non-integral pad models are run. It is not uncommon for non-integral pad models to take 15 minutes or more to process. To increase the memory allotted for NozzlePRO, the user will need to run the configuration file “cfng.exe”. This executable file should be located in the installation directory for NozzlePRO. Upon executing cnfg.exe, the following screen should appear.
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4.6.1
NozzlePRO
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Memory allocation is set inside the “J – Miscellaneous Settings” menu. The miscellaneous settings menu is shown below. The red arrow indicates the default memory allocation of 64Mb. Typically, this should be set to about 75% of the systems available memory. Be sure to pay careful attention to the necessary keys that save the changes.
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4.6.2
NozzlePRO 7.0
December 2006
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Chapter 5 – Section 1 Nozzle/PRO Fitness for Service Local thin areas and crack like flaws may be evaluated for most Nozzle/PRO geometries using the Nozzle/PRO fitness for service input form. Fitness for service evaluations are conducted using API 579 methodologies for Level 2 & Level 3 checks. Up to ten flaws may be defined for each model. To access the fitness for service options, click the “API 579 FFS” icon as shown below:
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5.1.1
NozzlePRO 7.0
December 2006
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Nozzle/PRO Fitness for Service Add New Flaw Additional flaws to be evaluated may be defined using the “Add New Flaw” button. Each time the “Add New Flaw” button is clicked, a new flaw will be added to the input form. Up to ten flaws may be defined.
Delete Current Flaw
User defined flaws may be deleted from the input form using the “Delete Current Flaw” button. To delete a flaw, first select the desired flaw from the flaw tabs and then click the “Delete Current Flaw” button.
Flaw Location Input Sheet The Flaw Location input sheet provides input to define the location, type, and geometry of the flaw.
Description The user may provide a descriptive name for each flaw.
Flaw Location The flaw location input is used to define the general location of the flaw on the model. Options are available for each region within the parent and attachment. The user should select the general region or area in which the flaw is located. Nozzle/PRO will use the maximum stress within the specified region and evaluate the flaw. The region in which the flaw will be located is highlighted in red within the images in the the lower left panel of the Fitness for Service screen. Copyright (c) 2007 by Paulin Research Group
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NozzlePRO 7.0
December 2006
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Evaluation Type The Evaluation Type input is used to specify the type of fitness for service evaluation desired. Available analysis types include local metal loss and crack like flaw evaluations. The user may also evaluate the defined flaw as both a local metal loss and crack like flaw to determine the worst case scenario.
Proximity to Weld The Proximity to Weld option provides the ability to specify the location of the flaw in relation to welds. The default selection is “Weld Region” and should provide a conservative evaluation. If the proximity to a weld is unknown, the user should consider using the “Weld Region” option. This flaw locator is not used for local thin areas, but is used for crack-like flaw evaluation. The effect of welds in local thin areas is included in the evaluation by the specification of the weld joint efficiency. For joint efficiencies of 1, the fact that the local thin area is in a weld has no effect.
Basis Each flaw must have a “Basis” defined so that the dimensions of the flaw may be determined. Here, the “Basis” input defines what procedure or input will be used to establish the dimensions of the flaw. Several options are available including: 1. Assume a default flaw size – Nozzle/PRO will assume that the flaw has a depth of 0.25 times the thickness of the material and a length equal to six times the thickness. 2. User defined flaw depth and length – the user must define the depth and length of the flaw which will then be used in the fitness for service evaluation. 3. Maximum measured flaw depth/length – this option should be used when a thickness measurement survey is available. In this case, the user will input the thickness survey data within the “Measurement Grid” sheet. Nozzle/PRO will determine the maximum depth and length based on the critical flaw depth and lengths using API 579 procedures. The maximum depth and length will be used irrespective of whether they are defined for the circumferential or longitudinal directions.
Flaw Depth Defines the maximum depth of the flaw. Only used when the flaw basis is “User Defined Flaw Depth and Length” Note that this input will be automatically generated when the flaw basis is the “Maximum measured flaw depth/length”.
Flaw Length Defines the maximum length of the flaw. Only used when the flaw basis is “User Defined Flaw Depth and Length”. Note that this input will be automatically generated when the flaw basis is the “Maximum measured flaw depth/length”.
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5.1.3
NozzlePRO 7.0
December 2006
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Measurement Grid The Measurement Grid input sheet is used to define the characteristics of local thin areas using an array of thickness measurements which encompass the flaw. Note that the Measurement Grid input sheet is only used when the flaw basis has been specified as “Maximum measured flaw depth/length” (see Flaw Location input discussion for more details).
Inside Diameter at Flaw The inside diameter of the shell at the location of the flaw. The inside diameter is used to calculate the length over which thickness averaging will be conducted.
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5.1.4
NozzlePRO 7.0
December 2006
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Min Req’d Thk Nominal Thk The minimum required thickness (left input box) and the nominal thickness (right input box) at the flawed location.
Future Corrosion Allowance Defines the future corrosion allowance for the flawed location. The future corrosion allowance is used in conjunction with the minimum required thickness and thickness survey data to determine maximum flaw dimensions. The future corrosion allowance should be based on operating experience, inspection data, and corrosion rate estimates. The future corrosion allowance is applicable to the expected future operating period.
Remaining Strength Factor The Remaining Strength Factor is the ratio of the strength of the damaged component to the undamaged component. Here, “strength” relates to the resistance against a limit type load to cause collapse or catastrophic failure. API 579 recommends an RSF factor of 0.90 for equipment in process services. Essentially, the remaining strength factor relates the strength of the damaged component to that of the undamaged component. Therefore, lower RSF values indicate that the analyst is willing to permit the equipment to operate a much lower strength than originally intended. Higher values are more stringent in that the flaws must be of a less significant nature and thus produce strengths closer to the undamaged state.
# Circ. Points Spacing Defines the number of circumferential measurement planes along the longitudinal direction of the shell (left input box). The spacing distance along the longitudinal axis, between the circumferential planes, is defined in the right input box. See image below for details. As recommended by API 579, a minimum of five measurement points must be provided in both the longitudinal and circumferential directions. Users should refer to API 579 for the proper spacing of the measurement points.
# Long. Points Spacing Defines the number of longitudinal measurement planes in the circumferential direction of the shell (left input box). The spacing distance along the circumferential direction, between the longitudinal planes, is defined in the right input box. See image below for details. As recommended by API 579, a minimum of five measurement points must be provided in both the longitudinal and circumferential directions. Users should refer to API 579 for the proper spacing of the measurement points. Copyright (c) 2007 by Paulin Research Group
5.1.5
NozzlePRO 7.0
December 2006
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Thickness Measurement Input Spreadsheet After the measurement details described above have been provided, the thickness measurement spreadsheet should appear. The thickness measurement spreadsheet provides input spaces for all the circumferential and longitudinal thickness measurements. The user should enter the data from their thickness survey in the columns and rows indicated by C1, C2, etc and L1, L2, etc. The column titled “Long CTP” and row titled “Circ CTP” summarize the critical thickness profiles in the longitudinal and circumferential directions, respectively. The minimum measured thickness along the critical thickness profiles is highlight in red font. User defined values which coincide with the nominal thickness are shown in light gray font while values less than the nominal thickness are shown in black font.
Critical Flaw Dimensions Once all values have been specified in the thickness measurement spreadsheet, the critical flaw dimensions calculated per API 579 will be available. Maximum flaw dimensions are provided for both the circumferential and longitudinal directions as shown below. These are output results for the API 579 flaw size calculations and may not be modified by the user. Note that these output results are only visible once the user has completed all of the input fields in the “Measurement Details” frame and the thickness measurement spreadsheet is visible.
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5.1.6
NozzlePRO 7.0
December 2006
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Optional Input The optional input page provides additional control over the fitness for service evaluation. A description of these input fields is provided below.
Probability of Failure Defines the probability of failure for the user defined flaw. This input is only used for the analysis of crack like flaws. The probability of failure is used in conjunction with the “primary load certainty” input to determine the partial safety factors applied to the primary and secondary stresses (and other user defined flaw variables). Higher probability of failure values will result in greater partial safety factors, effectively increasing the design margins in the fitness for service evaluation and providing for a “safer” design. • • •
High is the most conservative assumption (lowest risk of failure). Medium is slightly less conservative (moderate risk of failure). Low represents the lowest margin against the mean failure curve (higher risk of failure)
The default value of HIGH equates to a margin of 4 standard deviations below the mean failure curve. Medium represents approximately three standard deviations below the mean failure curve. Low represents approximately two standard deviations below the mean failure curve.
Primary Load Certainty The primary load certainty relates to the coefficient of variation (COV) related to the uncertainty in the primary stress distribution. This input is only used for crack like flaw evaluations. Three options are available for the primary load certainty input: 1. Well Known – primary loads and stresses at the flawed zone are computed or measured and are well known. This option corresponds to a COV = 0.10. Copyright (c) 2007 by Paulin Research Group
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NozzlePRO 7.0
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2.
3.
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Reasonably Known – primary loads and stresses in the flawed zone are computed or measured and are reasonably well known. Here, the uncertainty is due to the possible variation in the loading or calculation methods. Uncertain / Random Loadings – calculated or measured primary loads and stresses are significantly uncertain. The uncertainty is a result of the unknown or random nature of the applied loading or estimates made in the calculation of the primary stresses.
Weld Joint Efficiency Defines the joint efficiency of the welded joint. When a crack like flaw is located at a welded region, the primary stresses will be divided by the weld joint efficiency. The weld joint efficiency typically ranges between 0.65 and 1.0.
Nominal Thickness at Flaw Typically, the nominal thickness at the flaw is determined by the thickness at the flaw as defined in the finite element model. However, the user may override the finite element model’s thickness such that the fitness for service calculations use the options “Nominal Thickness at Flaw” value. Note that this thickness will not modify the local thickness in the finite element model, it is only used in the fitness for service post processing calculations.
Material’s Nil Ductility Temperature The nil ductility temperature is only used for crack like flaw evaluations. Defines the nil ductility temperature for the material of construction in which the flaw is located. Used as the “reference temperature”, and defined as the temperature corresponding to a Charpy impact value of 15 ft-lb for carbon steels and 20 ft-lb for Cr-Mo steels. The Nil Ductility Temperature is not used for stainless steels. Note that if the nil ductility is actually zero degrees, then a value near zero but not exactly zero should be specified (for instance 0.1). A value of zero will not initialize the input and results in a default nil ductility value for the materials.
Local Radius of Curvature Defines the local radius of curvature of the vessel or pipe at the location of the user defined flaw. If no input is provided, then Nozzle/PRO will use the user defined value for the parent or attachment given in the main Nozzle/PRO screen.
Number of Operating Cycles Defines the estimated number of operating cycles for which the flaw will be exposed to during the anticipated future service life. The number of operating cycles is not the total cycles for the equipment. Instead, it is only the number of future cycles to which the flaw is exposed.
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5.1.8
NozzlePRO 7.0
December 2006
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Ignore Partial Safety Factors The partial safety factors are used to provide additional margin against failure in light of uncertainties in the loadings and calculations. On occasion, the analyst is more concerned with reducing the safety margin and estimating a more realistic margin against failure. In such cases, the user may evaluate the flaw without the use of the partial safety factors. Note that this input is only used for the evaluation of crack like flaws.
Flaw is Exposed to a Marine Environment Used for crack growth rate calculations only; does not affect the local thin area computations. Increases the crack growth rate for both stainless and carbon steels per API 579 F.5.3 by 4.4 times.
Flawed Region has been Post Weld Heat Treated This factor is only used in the evaluation of crack-like flaws and will reduce the effect of residual stress when the flaw is in the proximity of a weld. If PWHT has been performed the residual stresses in the weld are reduced to 20% of their non-PWHT values.
Secondary Loads are Applied Dynamically Only used for the evaluation of crack like flaws. Used when some portion of the operating load or secondary stress is applied dynamically. In this case the KIC value will be adjusted based on the temperature, and the Dynamic Ramp loading time. The user can override this calculation by entering the Dynamic Critical fracture toughness at operating temperature if a better value is available.
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5.1.9
NozzlePRO 7.0
December 2006
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Advanced Input The advanced input tab provides additional control over the material properties to be used in the FFS calculations. Mainly, control over the material properties relating to the evaluation of crack like flaws is provided.
Define known material properties for analysis If material properties for the material of construction are known, then select this option to access the material definition options. Nozzle/PRO provides the following options for material definitions:
Static Fracture Toughness Available only if the option “Fracture Toughness Values are Known” is selected. KIC value at operating conditions. This value will be estimated by the program based on the type of material input if not entered. Only used for crack type flaws.
Dynamic Fracture Toughness (KID) Available only if the option “Fracture Toughness Values are Known” is selected.
Copyright (c) 2007 by Paulin Research Group
5.1.10
NozzlePRO 7.0
December 2006
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KIC value at operating conditions for dynamic loadings. Only used if the “Secondary Loads are Applied Dynamically” check box is marked in the Optional input tab. If not entered the program will calculate a dynamic KIC based on loading time and temperature. Only used for crack-type flaws. Critical J Value Available only if the option “Use Critical J Value to Calculate Toughness” has been selected. If a J integral value is entered it will be used to compute the KIC per API 579 Appendix F.4.2. Only used for cracktype flaws.
CTOD Value from Test Available only if the option “Use CTOD Value to Calculate Toughness” has been selected. If a crack tip opening displacement value is available from a CTOD test of the material then this value may be entered as per API 579 Appendix F.4.2.
Charpy Impact Energy Available only if the option ‘Use Charpy Impacts to Calculate Toughness” has been selected. Enter the Charpy energy at operating temperature if available. This value can be converted into the KIC value to be used in crack-type flaw evaluations.
Fitness for Service Example The following example illustrates the API 579 fitness for service tool in Nozzle/PRO. This particular example is API 579 example 4.11.1 and will illustrate the evaluation of a localized corrosion region in a pressure vessel, removed from any gross structural discontinuities, but located at a longitudinal weld seam.
This sample model may be found in the “Samples1” folder of the installation directory with filename: “NozzlePRO_FFS_LTA.nozzlepro”
A region of localized corrosion has been found on a pressure vessel during a scheduled turnaround. The local metal loss area passes through a longitudinal weld seam. Design Conditions Inside Diameter Fabricated Thickness Uniform Metal Loss FCA Material Weld Joint Efficiency
= 300 psi @ 350F = 48 in. = 0.75 in. = 0.0 in. = 0.1 in. (Future Metal Loss [Corrosion Allowance]) = SA 516 Grade 70 = 0.85
The corroded area was NOT in the circumferential weld seam. Copyright (c) 2007 by Paulin Research Group
5.1.11
NozzlePRO 7.0
December 2006
Effective Longitudinal Flaw Length Effective Circumferential Flaw Length Minimum thickness
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= 9.75 in. = 9.0 in. = 0.45 in.
Thickness Measurements for the local metal loss are given below. There are 8 measurement points in the longitudinal (C) direction, and 7 measurement points in the circumferential (M) direction.
M1 M2 M3 M4 M5 M6 M7 Long CTP
Step 1
C1
C2
C3
C4
C5
C6
C7
C8
0.75 0.75 0.75 0.75 0.75 0.75 0.75
0.75 0.48 0.57 0.61 0.62 0.57 0.75
0.75 0.52 0.59 0.47 0.59 0.59 0.75
0.75 0.57 0.55 0.58 0.58 0.61 0.75
0.75 0.56 0.59 0.36 0.57 0.57 0.75
0.75 0.58 0.60 0.58 0.48 0.56 0.75
0.75 0.60 0.66 0.64 0.62 0.49 0.75
0.75 0.75 0.75 0.75 0.75 0.75 0.75
0.75
0.48
0.47
0.55
0.36
0.48
0.49
0.75
Circ CTP 0.75 0.48 0.55 0.36 0.48 0.49 0.75
Specify geometry for the pressure vessel. Note that the option “No Attachment” has been selected since the flaw is located in the shell removed from any gross structural discontinuities.
Step 2
Click “Loads” to define the loadings acting on the pressure vessel. Input the values given below. When finished, click OK to return to the main Nozzle/PRO interface.
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5.1.12
NozzlePRO 7.0
Step 3
December 2006
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Click “Materials” to define the material of construction for the pressure vessel shell. Once finished, click OK to return to the main Nozzle/PRO interface screen. Users with a Mat/PRO license may use the “Import Material from Mat/PRO” button to import all of the material properties. Otherwise, simply input the values given below:
Step 4
Open the API 579 FFS definition screen by clicking the API 579 FFS icon:
Step 5
In the API 579 FFS input form, define a description and select the Flaw Location. Note that only one option is available in the Flaw Location list. This is because the Nozzle/PRO attachment type was “No Attachment”.
Step 6
Since the flaw to be evaluated is a local corroded region, select the option “Local Metal Loss” from the evaluation type input field.
Step 7
The flaw is located in a welded region, therefore the option “Weld Region” must be selected for the Proximity to Weld input field.
Copyright (c) 2007 by Paulin Research Group
5.1.13
NozzlePRO 7.0
Step 8
December 2006
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Define the flaw definition basis. This input instructs Nozzle/PRO how the flaw dimensions will be provided. In this example, a thickness survey has been provided and will be used in the flaw evaluation. Therefore, the option “Maximum measured flaw depth/length” should be selected. When “Maximum measured flaw depth/length” is selected, Nozzle/PRO will expect the user to provide a thickness survey input in the Measurement Grid input tab. Nozzle/PRO will use the largest flaw dimensions in circumferential and longitudinal directions in the FFS calculations.
Step 9
Click the Measurement Grid tab to access the thickness survey input form.
Step 10
In the Measurement Grid input tab, fill in the various input fields as shown below:
Step 11
Fill in the Thickness Survey spreadsheet with the thickness measurements provided at the beginning of this example: Note that the critical thickness planes (CTP’s) in the circumferential and longitudinal directions will be determined as the input is completed. Also, the minimum measured thickness is highlighted by red font.
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5.1.14
NozzlePRO 7.0
December 2006
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Step 12
Once all of the thickness survey data is entered, the flaw size calculations should be available in the Critical Flaw Dimension results frame. The maximum of either the circumferential or longitudinal dimensions will be used in the calculation. Recall that these will be automatically inserted in the Flaw Depth and Flaw Length input fields as discussed in Step #6.
Step 14
Click the “Optional” input tab to define any option input values.
The only requirement for this example is the Weld Joint Efficiency. Nozzle/PRO defaults to a Weld Joint Efficiency value of 0.70. However, in this example the Weld Joint Efficiency is 0.85.
Step 15
Click OK to save the flaw data and return to the main Nozzle/PRO input screen.
Step 16
In the main Nozzle/PRO interface screen, click “Plot Only” to generate a graphical plot of the model to be analyzed. The result should be as shown below:
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5.1.15
NozzlePRO 7.0
Step 17
December 2006
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When the graphical image appears, the portions of the model to be included in the FFS calculations can be reviewed using the “FFS” menu option. The nodes of the model to be included in the FFS calculation will be highlighted by the maroon colored dots as shown below. Close the plot window when finished viewing the model.
Step 18
In the main Nozzle/PRO screen, click Run FE to perform the finite element analysis and FFS calculations.
Step 19
After the analysis has completed, the API 579 Fitness for Service calculations will be available in the output report. To access the reports, click on the following menu items in the report’s table of contents:
Refer to the following discussion for interpretation of the analysis results.
A Pass/Fail summary of the FFS calculations is provided in the FFS Results Summary report. This report provides a quick review of the calculation results for each of the user defined flaws. In this example, the summary report tells the user that Flaw #1 (the local thin area defined in this example) is not acceptable and exceeds the allowable limits by a factor of 1.331.
Copyright (c) 2007 by Paulin Research Group
5.1.16
NozzlePRO 7.0
December 2006
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Details of the FFS calculations for Flaw #1 can be reviewed by clicking the “FFS for Flaw# 1 for Region: Cylindrical Shell” link in the report’s table of contents. This report is shown below.
FFS for Flaw# 1 for Region:Cylindrical Shell API 579 Fitness for Service Evaluation -----------------------------------------------Conservative assumptions were made when implementing the fitness for service rules of API579 Sections 5.0 and 9.0. It is the users responsibility to review and check the results printed herein to verify that they apply and are valid for the particular problem studied. Descr:
API 579 Example 4.11.1 (Corros
Yield Stress at Room Temperature Yield Stress at Operating Temperature Flow Stress at Operating Temperature Flow Stress at ROOM Temperature Modulus of Elasticity at Room Temperature Modulus of Elasticity at Operating Temperature
= = = = = =
Internal Pressure Operating Temperature
= =
Local Local Local Local
= = = =
10.118 1.292 0.003 0.007
ksi ksi ksi ksi
= = = =
0.387 4.355 0.750 24.750
in. in. in. in.
Primary Membrane Stress in Area of Flaw Primary Bending Stress in Area of Flaw Secondary Membrane Stress in Area of Flaw Secondary Bending Stress in Area of Flaw
Initial Crack Depth Initial Crack Half-Length Component Wall Thickness at Flaw Component Inside Radius at Flaw Location
38.000 33.050 43.050 48.000 29400.000 28100.000
ksi ksi ksi ksi ksi ksi
300.000 psi 350.000 degF
Flaw is in an area that contains a weld or HAZ. Longitudinal Weld Joint Efficiency Probability of Failure
= 0.850 = 0.000001000
Coefficient of Variation (Primary Loads and Stresses are computed and well known.)
=
0.100
Poissons Ratio used in this analysis
=
0.300
API 579 Section 5.0 Assessment for Local Metal Loss --------------------------------------------------5.54 Membrane Stress due to Primary Loads 5.54 Allowable Stress due to Primary Loads
= =
Primary Membrane Stress at Flaw EXCEEDS limit
=
5.54 Membrane Stress due to Secondary Loads 5.54 Allowable Stress due to Secondary Loads
= =
0.009 ksi 49.575 ksi
Secondary Membrane Flaw Stress WITHIN allowable
=
0.017 %
Copyright (c) 2007 by Paulin Research Group
32.992 ksi 24.788 ksi 133.100 %
5.1.17
NozzlePRO 7.0
December 2006
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Chapter 5 – Section 2 Nozzle/PRO Piping Input Screens Piping may be attached to Nozzle/PRO shell models using the piping input screens accessed via the “Piping Runs…” icon as shown below. Up to ten unique piping runs may be included with the Nozzle/PRO model.
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NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping All piping is modeled using the Nozzle/PRO Piping input form. Each of the inputs will be described in the following sections.
Create New Piping Run
Additional piping runs are created using the “Create New Piping Run” button. Each time the “Create New Piping Run” button is clicked, a new piping run tab will be added to the input form. Up to ten unique piping runs may be defined for the model. Each piping run may contain virtually any number of piping segments (elements).
Delete Current Piping Run
Piping runs may be deleted from the input form using the “Delete Current Piping Run” button. The piping run which will be deleted will be the active piping run currently selected in the piping tab sheet.
Options There are a number of optional settings the user may specify which will control the Nozzle/PRO piping solution and reports. These options are accessed via the “Options” button.
Plot Model Copyright (c) 2007 by Paulin Research Group
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NozzlePRO 7.0
December 2006
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Prepares the model for analysis and generate a graphical plot of the model. The user may also click the “Plot Only” button in the main Nozzle/PRO interface screen to achieve the same results.
Pipe Run Tabs Each tab indicates a piping run included in the Nozzle/PRO model. Access the input for the specific piping run by selecting one of the available pipe run tabs.
Duplicate Row
Used to duplicate an existing input row in the piping input spreadsheet.
Add Row
Add a new row to the piping input spreadsheet.
Delete Row
Delete the active row from the piping input spreadsheet.
Edit Row
Use the Edit Row button to perform various editing operations on the current row and piping input spreadsheet such as cut, copy, paste, insert, etc.
Text Input… (or Grid Input…)
The user may construct each piping run using either the standard spreadsheet input or a raw text file with Beamer file commands. To switch into text input mode, just click the Text Input button. Nozzle/PRO can convert the existing spreadsheet input into text input, but can not convert text input back into the spreadsheet input. Therefore, any changes made in the Text Input mode can never be converted back into the Grid Input mode. The user may switch between Text Input mode and Grid Input mode without losing either input. For instance, even when Text Input mode is being used, the original spreadsheet data will be saved so that the user can revert back at any time. However, keep in mind that the spreadsheet will not be revised with any Text Input changes.
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5.2.3
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Grid Input The Grid Input mode is the primary input mode and recommended for most users. The Grid Input mode allows the user to construct the Nozzle/PRO piping model using a familiar spreadsheet input format. The following describes the input fields available for the Grid Input mode.
Element Type
Designates the finite element type to be used in the piping model. Two element types are available, the standard 6 DOF beam elements or an advanced 18 DOF beam element. The 6 DOF beam element is widely used in piping analysis programs and will replicate traditional piping analysis results. The advanced 18 DOF piping element permits ovalization degrees of freedom and therefore produces more accurate solutions where local flexibilities are important such as in large D/t piping. The 18 DOF elements also produce more accurate stiffness interaction results for close coupled elbow-elbow pairs and intersection models.
Description The user may provide a descriptive name for the current piping run here.
Start at Shell Model Each piping run must begin at a defined location in the model. The “Start at Shell Model” is used to begin a piping run from an attachment point on the Nozzle/PRO shell model. Options are typically at the end of the nozzle or some point on the parent geometry (ends of the header or bottom of a head, etc).
Start at Node Piping runs may also begin from intersection locations within other piping runs. This option will typically be used when the user needs to construct branch piping intersections. The selection list here is a listing of all “End Nodes” defined in other piping runs. End nodes must be defined within other piping runs before a new piping run can be created and begin from an existing “End Node”.
Piping Input Spreadsheet
The piping input spreadsheet allows the user to construct the piping model. Each row represents a segment within the piping run. For instance, a straight section of piping would be defined by its length, diameter, and other properties. The various columns within the Piping Input Spreadsheet are described below:
Input Column Description X Length
Description The description field should be used to provide a unique identifier for the piping input row which will help the user when reviewing the input or results at a later date. Describes the length of the piping segment in the global X direction. For straight sections, this is the length to the ends of the straight section or to the tangent
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5.2.4
NozzlePRO 7.0
Y Length
Z Length
OD Thk
Material End Label (Optional)
Pressure Temperature Fluid Density Restraints End Forces
Bend at End?
Bend Radius Flanged Ends Number Miter Cuts Rigid Element? Rigid Weight
Insulation Thickness Insulation Density Refractory Thickness Refractory Density No Output
December 2006
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intersection points if a bend is located at the end of the straight section. Describes the length of the piping segment in the global Y direction. For straight sections, this is the length to the ends of the straight section or to the tangent intersection points if a bend is located at the end of the straight section. Describes the length of the piping segment in the global Z direction. For straight sections, this is the length to the ends of the straight section or to the tangent intersection points if a bend is located at the end of the straight section. Describes the outside diameter of the piping segment. Describes the design thickness of the piping segment. This thickness should be the nominal thickness of the pipe less any mechanical tolerances, corrosion allowance, or other margins. Specify the material of construction for the piping segment. See the Piping Material input screen for further description. • The end label is used to define a connection point for other piping runs. For instance, end node labels are typically defined where other piping runs will begin or end. These are usually where piping branch intersections occur. • The End Label may be a Base Node ID defined as part of a restraint in another portion of the piping model. If the End Label is a Base Node ID, then the two nodes will be tied together by the stiffness defined for the restraint containing the Base Node ID. • This input is optional. The operating pressure for the piping segment. The operating temperature for the piping segment. Describes the density of the contents of the piping segment. If a fluid density is provided, Nozzle/PRO will assume that the entire piping segment is filled. Used to apply restraints to the piping segment. See the Piping Restraints screen for more details on this feature. Define any point loads using this input option. The end loads will always be applied at the end of the current piping segment. For piping segments with bends at the end, the end forces are applied with the same philosophy as the restraints. If a piping bend exists at the end of the piping segment, then mark this check box. All bends are assumed to be standard bends with a bend radius equal to 1.5 times the outside diameter of the piping segment. The user may override the default bend radius of 1.5*D by specifying a user defined bend radius in this field. If rigid components exist near the bend which may influence the flexibility of the bend, then select the number of ends affected by these rigid components. For mitered bends, specify the number of miter cuts which exist along the bend. If the current piping segment should be considered a rigid element, then mark the Rigid Element check box. For rigid elements only, the user may define the total weight of the rigid element. If the rigid weight is specified as zero, then Nozzle/PRO will assume that a rigid construction element should be generated. If the rigid weight is greater than zero, then the total weight of the rigid will be equal to the specified rigid weight. If external insulation exists on the piping segment, define the thickness of the insulation here. Describes the density of the piping insulation. If internal refractory exists on the piping segment, define the refractory thickness here. Describes the density of the piping refractory. Permits the user to turn off output reporting for the selected pipe segment. If selected, then the piping segment will not be reported as part of the solution report. This is typically used for rigid construction elements where the results are not of interest.
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5.2.5
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Text Input The second input mode available for constructing Nozzle/PRO piping models is the Text Input mode. In the Text Input mode, Beamer command text strings are used to instruct Nozzle/PRO how to construct the piping model. This input method is only recommended for advanced users familiar with the Beamer input file command system. Users can gain experience by first constructing the model using the Grid Input mode and then converting to Text Input mode as described below. It is highly recommended that user’s attempting to utilize the Text Input mode refer to the Text Input mode help file by clicking the “Text Help” button. New and experienced users may find it convenient to use the “Insert New Command” option. This option provides a simple interface to construct and insert the various Beamer commands into the Text Input mode. The Command Builder interface permits the user to input familiar information while letting Nozzle/PRO take care of the proper formatting of the various Text Input commands.
When switching into Text Input mode, Nozzle/PRO will display the following warning message. This message is intended to warn the user that any input or changes provided in the Text Input mode can not be converted back into the Grid Input spreadsheet. The original spreadsheet input data will remain available, but will not be revised with the Text Input revisions.
If existing spreadsheet input is already available, then the user will be presented with an opportunity to convert the spreadsheet input data into Text Input. This is often useful if the user wishes to quickly construct the model using the Grid Input mode and then make final alterations using the Text Input method prior to analysis. It is also useful when learning to use the Text Input mode since the converted spreadsheet data provides a good example to follow. • Click YES to convert the existing Grid Input data into the Text Input format. • Click NO to start with a clear Text Input format. • Click Cancel to quit and return to the Grid Input mode.
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NozzlePRO 7.0
December 2006
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Insert New Command…
Launches the Command Builder interface. This allows the user to construct and insert Beamer commands into the Text Input interface without having to learn the strict format required for by the Text Input mode.
Error Check
When Text Input mode is being used, it is easy to make simple input errors. The Error Check button will perform an error check on the text input and open the error report file for the user to review. It is recommended that this is used frequently and before any analysis is attempted.
Plot Input
Generate a graphical plot of the current input when using the Text Input mode.
Text Help…
Opens the Beamer command help file.
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5.2.7
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Material List The Nozzle/PRO Piping Material List is used define all piping materials which will be used in the piping models.
Add Row
Additional materials may be defined using the Add Row button. Clicking the Add Row button will create a new input row in the Material Spreadsheet.
Delete Row
Materials may be deleted from the input form using the “Delete Row” button. The material which will be deleted is the active row in the material spreadsheet.
Material Input Spreadsheet
The material input spreadsheet allows the user to define unique materials to be used in the piping model. Each row represents a different material. The material properties are described using the various columns of the spreadsheet. Each of these material property columns is described in the following table:
Input Column Material Description
Cold Allowable
Description Provides a unique description for each material defined in the material spreadsheet. This description will be available in the piping input spreadsheet when each piping segment is assigned a material of construction. Defines the cold allowable stress for the material. The cold allowable should be the
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5.2.8
NozzlePRO 7.0
Hot Allowable Elastic Modulus Poisson’s Ratio Expansion Coefficient Density Cold Yield Hot Yield Cold Tensile
December 2006
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allowable stress at the minimum temperature of the operating cycle. Defines the hot allowable stress for the material. The hot allowable should be the allowable stress at the maximum temperature of the operating cycle. Specify the elastic modulus of the material. Defines the Poisson’s ratio of the material. Defines the thermal expansion coefficient of the material. This should be the mean thermal expansion between 70°F (21°C) and the operating temperature. Specify the density of the material. Defines the cold yield stress for the material. The cold yield should be the allowable stress at the minimum temperature of the operating cycle. Defines the hot yield stress for the material. The hot yield should be the allowable stress at the maximum temperature of the operating cycle. Defines the cold tensile strength for the material. The cold yield should be the allowable stress at the minimum temperature of the operating cycle.
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5.2.9
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Restraints The Piping Restraints input form is accessed through the Nozzle/PRO Piping Input form’s piping spreadsheet using the pop-up button in the specified piping segment.
Restraints column. The Piping Restraints input form is used to apply restraints to a
Add Row
Additional piping restraints may be defined using the Add Row button. Clicking the Add Row button will create a new input row in the Piping Restraints spreadsheet.
Delete Row
Restraints may be deleted from the input form using the “Delete Row” button. The restraint which will be deleted is the active row in the material spreadsheet.
Input Column Restraint Type Location
Stiffness
Initial Load
Description Select the type of restraint to be applied to the piping segment. Defines the location for the restraint on the piping segment. The default (blank) is to apply the restraint to the “TO” end of the piping segment. The user may specify that the restraint should act at the “FROM” end of the piping segment by selecting the option “Start Node” Optional Defines the translational or rotational stiffness of the user defined restraint. A default value of 1e15 will be used if no stiffness is specified. This option will typically be used to define a spring can or hanger with known spring stiffness. In this case, the user should define the linear spring stiffness defined by the manufacturer. Optional Defines the initial load acting on the restraint. A common application of this input field is to define a spring support with an initial load.
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5.2.10
NozzlePRO 7.0
Base Node ID
Displacement Case
Displacement
Cos X Cos Y Cos Z Notes
December 2006
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Optional The Base Node ID is used to tie degrees of freedom together between various portions of the model using the defined stiffness value. Optional Use to define the load case in which the displacement acting on the restraint will be applied. Note that displacements may only be defined for directional restraints such as X, Y, Z, Rx, Ry, and Rz. Displacements are not permitted for restraint types such as ANCHOR. If the user wishes to define a displacement on an anchor, then the anchor must be defined by six independent restraints (one for each degree of freedom), each with their own properties. Optional Defines the displacement magnitude to be applied to the restraint. See Displacement Case description above for additional considerations. Optional The vector component in the Global X direction for a skewed restraint type. Optional The vector component in the Global Y direction for a skewed restraint type. Optional The vector component in the Global Z direction for a skewed restraint type. Optional Insert any descriptive text here to clarify the purpose of the restraint. These notes will appear as part of the output report and input echo.
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5.2.11
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Loads The Piping Loads input form is accessed thru the Nozzle/PRO Piping Input form’s piping spreadsheet (see the End Forces column in the piping spreadsheet discussion). The piping loads input form is used to define applied forces acting on the end of the selected piping segment. All loads are defined in the global coordinate system and applied at the end of the specified piping segment.
Weight Loads Weight loads include any sustained type loads acting in the installed case. Operating Loads Operating loads are any applied loads which are present during the operating case being evaluated. The operating loads should include the weight loads defined above. The difference between the operating loads and weight loads will be used to define the range case for fatigue analysis. Occasional Loads Occasional loads are usually due to wind, seismic, or other cases not defined as part of the typical operating conditions. Occasional loads can be evaluated either as contributing to primary type failures or fatigue failures. See Section 2 of the Nozzle/PRO manual for more discussion of these options. Note that the occasional loads should not include any portion of the weight or operating load cases. The occasional loads will be combined automatically by Nozzle/PRO where appropriate.
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5.2.12
NozzlePRO 7.0
December 2006
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Nozzle/PRO Piping Preferences Several options are available for controlling the solution and output format when using the Nozzle/PRO piping feature. The Nozzle/PRO Piping Preferences input form may be accessed through
Piping Model Only A piping only model with no Nozzle/PRO shell elements may be created by selecting this option. This option is typically used when the user wishes to analyze the piping elements only without including any shell model as part of the solution.
Include Pressure Stiffening on Bends Indicates whether the pressure stiffened flexibility factors should be used according to ASME B31.3. The default is to include pressure stiffening effects.
Do not break down… By default, Nozzle/PRO will break piping segments into several elements in the FEA analysis. This is to improve the stiffness model and dynamic solutions. The user may specify that the piping segments are not broken down into multiple elements by selecting this option.
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NozzlePRO 7.0
December 2006
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Include Fluid Weight Defines whether or not fluid weight should be included in the piping analysis.
Include Self Weight Defines whether or not weight loads due to material density should be included in the piping analysis.
Rigid Element OD Multiplier Controls the diameter of rigid elements in the piping model. Note that this option will not be considered for rigid elements where the rigid weight has been specified as zero since these elements are represented as weightless rigid links in the model. Also, the rigid element OD multiplier will only affect the stiffness (via the element thickness) of the rigid piping element and not the weights calculated for the rigid.
Include Insulation Weight on Rigid Piping Elements Determines whether or not weight due to insulation will be added to the user defined rigid element weight. The insulation weight included on the rigid will be 1.75 times the weight of insulation on equivalent straight pipe.
Include Refractory Weight on Rigid Piping Elements Determines whether or not weight due to refractory will be added to the user defined rigid element weight. The refractory weight included on the rigid will be 1.75 times the weight of refractory on equivalent straight pipe.
Input Echo Report Options
Input Echo Report Option Full input echo Include only non-null values in input echo
Include minimal input echo
Do not include input echo
Description All available input fields will be reported in the user input echo report. Only input fields which contain input explicitly defined by the user will be included in the input echo. Null fields will not be included as part of the input echo report. Only non-null unique values will be reported. Input values common between adjacent input rows in the piping input spreadsheet will not be included in the input echo report. This option will provide the most efficient output report since only the pertinent input is reported. No input echo will be included as part of the solution report.
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5.2.14
NozzlePRO 7.0
December 2006
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Chapter 5 – Section 2 Piping Example #1- Using End Node Labels The following example will illustrate the basic steps necessary to construct simple piping geometries attached to the Nozzle/PRO shell models. In this example, the piping layout as shown below will be used to demonstrate the usual input operations. For simplicity, default material properties will be used for the vessel, nozzle, and attached piping.
This sample model may be found in the “Samples1” folder of the installation directory with filename “NozzlePRO_Piping.nozzlepro” In this example, several key concepts will be covered: • Creating “End Node Labels” which permit individual piping runs to connect to one another. In this example, Piping Run #2 begins at a branch connection along Piping Run #1 and also ends at a branch connection along Piping Run #1. • Creating multiple boundary conditions at the end of a single piping segment. Using the piping restraint screen, multiple restraints may be applied to any piping segment.
The first step is to construct the shell element model of the vessel and nozzle, where the first piping run will be attached. In this case, the vessel is 60” OD x 0.625” with a 12.75” OD x 0.375” x 14.0” long nozzle. A screen shot of the vessel input values are given below.
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5.2.15
NozzlePRO 7.0
December 2006
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Once the vessel and nozzle geometry has been defined, the remaining work is to define the geometry of the attached piping runs. The following steps outline the general procedure to construct the piping model: 1.
Click the “Piping Runs…” icon in the main Nozzle/PRO interface, located just above the nozzle geometry input frame.
2.
Since Piping Run #1 will begin at the end of the nozzle, select the option “Start at Shell Model” and then select “End of Nozzle” from the drop down list.
3.
Input the dimensions and geometry info for Piping Run #1. The inputs for Piping Run #1 are shown below. Some important features to note are: a. To create a new row in the spreadsheet, click the “Add Row” icon in the toolbar. b. The first pipe segment, which is the length between the nozzle and the intersection to Piping Run #2, has an “End Label” defined at the end of the pipe segment. This end node label defines a connection point where other piping nodes may be attached. In this example, Piping Run #2 will begin from End Label “A”. c. Note that Row #12 also has an “End Label” defined. In this case, the end label is “B”. End Label “B” will be the termination point for Piping Run #2. d. Restraints are created by selecting the blinking button in the Restraints column. i. When the piping restraints form appears, click “Add Row” to create a new piping restraint then select the appropriate restraint type and fill in the remaining properties for that restraint. e. Note that some input items are column duplicated. Column duplicated row entries are indicated by the light gray text. For instance, the pipe OD is defined only for the first input row and this defined value is automatically inherited by each row following.
Input for Piping Run #1 in Example
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NozzlePRO 7.0
December 2006
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Sample Piping Restraint for a Global Y Restraint in Piping Run #1.
4.
After completing all the input for Piping Run #1, click the “Create New Piping Run” button to create a new input tab sheet for Piping Run #2. This should add a new tab to the tab list with title “Pipe #2”.
5.
Since Piping Run #2 will begin from a node within another piping run and not a point on the shell model, select the “Start at Node” option and set the starting node label to “A”.
6.
Next, input the piping geometry for Piping Run #2. The input spreadsheet should be as shown below for Piping Run #2: a. Important – Piping Run #2 intersects Piping Run #1 and ends at the branch connection within Piping Run #1. Therefore, Piping Run #2 must connect to End Label “B” which was previously defined in Piping Run #1 To connect to node “B”, the End Label in row 7 is defined as “B” as shown below. b. Global Y & Z restraints have been provided in the Restraints column for Rows #2 and #3 This is indicated by the word “Multiple”. Click on the blinking button to define the multiple restraints to applied to the piping model. An example of the Global Y and Z restraints are given below.
Input for Piping Run #2 in Example
Example of Global Y & Z Restraints for Piping Run #2
7.
After all of the piping model input has been specified, click CLOSE to return to the main Nozzle/PRO interface. The model may now be plotted or analyzed as normal with Nozzle/PRO models. A plot of the above input should yield the following model:
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5.2.17
NozzlePRO 7.0
December 2006
Copyright (c) 2007 by Paulin Research Group
www.paulin.com
5.2.18
NozzlePRO 7.0
December 2006
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Piping Example #2 – Using Base Node ID’s The following example will illustrate the use of Base Node ID’s in Nozzle/PRO piping models. Base Node ID’s are defined in the Piping Restraint screens and can be used in the piping input spreadsheet or within other Piping Restraint definitions. The Base Node ID’s tie specific degrees of freedom (translational or rotational) together. In this example, the goal is to tie two piping runs together to simulate a lower pipe supported from the upper pipe as shown below. The upper and lower pipes will be tied together using a user defined Base Node ID.
This sample model may be found in the “Samples1” folder of the installation directory with filename: “NozzlePRO_Base_Node.nozzlepro”
This example will illustrate the following concept: • Creating “Base Node IDs” which are used to tie degrees of freedom together. In this example, Pipe Run #1 will be “slaved” to Pipe Run #2 in the Global Y direction thru Base Node ID “Spring”. • Applying user defined loads to the piping model.
Copyright (c) 2007 by Paulin Research Group
5.2.19
NozzlePRO 7.0
December 2006
www.paulin.com
The first step is to construct the shell element model of the vessel and nozzle, where the first piping run will be attached. In this case, the vessel is 60” OD x 0.75” with a 18.0” OD x 0.375” x 20.0” long nozzle. A screen shot of the vessel input values are given below.
Once the vessel and nozzle geometry has been defined, the remaining work is to define the geometry of the attached piping runs. The following steps outline the general procedure to construct the piping model: 1.
Click the “Piping Runs…” icon in the main Nozzle/PRO interface, located just above the nozzle geometry input frame.
2.
Since Piping Run #1 will begin at the end of the nozzle, select the option “Start at Shell Model” and then select “End of Nozzle” from the drop down list.
3.
Input the dimensions and geometry info for Piping Run #1. The inputs for Piping Run #1 are shown below. Some important features to note are: a. To create a new row in the spreadsheet, click the “Add Row” icon in the toolbar. b. The first pipe segment, which is the length between the nozzle and the intersection to Piping Run #2, has an “End Label” defined at the end of the pipe segment. This End Label is defined as “Spring1”, which will be the same name assigned to the Base Node ID in Piping Run #2. Therefore, by defining “Spring1”, the pipe segment will be slaved to Piping Run #2 thru Base Node ID “Spring1”.
Input for Piping Run #1
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4.
After completing all the input for Piping Run #1, click the “Create New Piping Run” button to create a new input tab sheet for Piping Run #2. This should add a new tab to the tab list with title “Pipe #2”.
5.
Piping Run #2 will begin from the top of the shell model. Therefore, the appropriate selection for the start location is “Start at Shell Model” with the location designated as “Top of Parent”.
6.
Next, input the piping geometry for Piping Run #2. The input spreadsheet should be as shown below for Piping Run #2 (see image of input screen below for additional guidance): a. Important – In Row #2, the Global Y restraint with the Base Node ID which ties Piping Run #2 and Piping Run #1 together must be defined. To do this, follow these steps: i. Open the Piping Restraints screen selecting the cell in Row #2 within the “Restraints” column, then click the blinking arrow button. ii. When the Piping Restraints screen appears, click “Add Row” to generate a new restraint for the pipe segment. iii. Since the restraint should act in the Global Y direction only, select “Global Y” from the Restraint Type column. iv. The spring which is being simulated will have a linear stiffness of 1.0e5 lbf/inch. Specify this value in the Stiffness input column. v. Specify the Base Node ID which is used to uniquely identify this Base Node. In this example, the Base Node ID is “Spring1”. Recall that this same variable name was used as the End Label within Piping Run #1. Now that the Base Node ID and restraint is created, Piping Run #1 and Piping Run #2 are tied together by the user defined stiffness in the Global Y direction. vi. Click OK to return to the main piping input form. Piping Input for Piping Run #2
Piping Restrain Input for Piping Run #2, Row #2
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December 2006
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To illustrate the way in which the degrees of freedom will be tied together between Piping Run #1 and #2, the user can apply two directional loads to the free end of Piping Run #2. One load will be in the Global Y direction and one load in the Global Z direction. To define these end loads, use the following steps: a. In Row #3, the last input segment for Piping Run #2, click on the cell within the column End Forces, then click the blinking arrow button . b. When the Piping Loads screen appears, specify 10,000 lbf in the weight case for the Global Y and Global Z directions, in the Weight and Operating load cases. c. Click OK to return to the main piping input form.
Piping Restrain Input for Piping Run #2, Row #3
8.
All of the input should now be complete. Next, click the RUN FE button in the main Nozzle/PRO interface screen to run the analysis. The results should indicate that only the Global Y degree of freedom has been linked between Piping Run #1 and #2. a. Since only the Global Y direction degree of freedom is tied between Piping Run #1 and #2, there should only be displacement in the Global Y direction for Piping Run #1. There should be no displacement in the Global Z direction (other than a very small amount translated thru the shell model due to torsion loading of the shell model by Piping Run #2). b. Results from the FEA are shown below. Global Y displacements are shown in the figure at left. As expected, the Base Node has tied the Global Y degree of freedom between Piping Run #1 and #2, resulting in Y displacements. Since the Base Node has only linked the Global Y displacement, there are no other displacements translated through the base node tie. Therefore, even though a Z direction load is applied to Piping Run #2, it is not translated to Piping Run #1 as shown in the right-hand figure.
Left – Global Y displacement showing affect of Base Node. Loads are transferred in Global Y direction. Right – Global Z displacement. Note that Base Node did not transmit Global Z loads or displacements.
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5.2.22
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Chapter 5 – Section 3 Axisymetric 2d and Brick Models Axisymetric 2d and Brick models may be constructed for spherical, elliptical, dished or conical heads. (Although there are some restrictions for conical heads.) Nozzles can only be in the center of axisymetric 2d head geometries but may be shifted off-center for brick axisymetric models. Axisymetric models are selected by clicking the Axisymetric Heads and Skirts radio button on the Options form. Text boxes on the other NozzlePRO forms that do not apply for axisymetric models are grayed. Some typical axisymetric model geometries are shown below:
There is extensive help shown below:
throughout the axisymetric modeling data screens. The main axisymetric data form is
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Several examples will best display the recommended uses for the axisymetric 2d and brick modeler. Start with a basic elliptical head and center manway nozzle description.
Enter a pressure of 1750 psi.
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And a 1.25 inch fillet between the nozzle and head. Since we plan on radiusing the fillets, reduce the stress concentration from 1.35 to 1.1.
The default model is a 3d shell model. The D/T ratio is 40/2 = 20 for the head. The default shell model and peak outside and inside stresses are shown below.
The large white zone in the middle between the nozzle and the outer ring is the “weld zone,” which is inside the material. The shell model attempts to compute the stresses where failure most often occurs in an externally loaded, and pressurized geometry, which is on the outside surface at the toe of the fillet. To check these stresses using the axisymetric modeler click on the Axisysymetric Heads and Skirts radio button, and then set the model to analyze a nozzle in a top head. Click the check boxes for adding a radius to the inner and outer corners, and since Copyright (c) 2007 by Paulin Research Group
5.3.3
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the boundary condition is apparently affecting the inside peak stress at the edge of the nozzle put a blind flange boundary condition on the end of the nozzle. NozzlePRO will design a flange so that the flange ring bending stresses are within allowables, and then select other thicknesses according to good proportions, so the flange dimensional data can be left blank. The inputs for this model are shown below.
The results from the axisymetric 2d calculation are shown graphically below:
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5.3.4
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The 3d viewer can be used to interrogate the stresses more carefully, since we are interested in seeing how close our shell model results match the axisymetric model results.
The high stress pointer clearly shows that the highest stress in the nozzle is on the outside at the nozzle to shell junction at the toe of the radiused weld. The stress at the flange attachment is also seen to be higher on the inside than on the outside as shown in the shell model, but is only seen to be about 10,452 psi. The stress output from the axisymetric 2d and brick analysis is the stress intensity range. The stress intensity range is twice the alternating peak stress intensity which is the stress used in ASME Section VIII Division 2 Appendix 5 as Pl+Pb+Q+F, so to find Pl+Pb+Q+F for comparison against Code fatigue curves, and for comparison with NozzlePRO Pl+Pb+Q+F calculations the peak stress intensity range must be divided by 2: 33,631 / 2 = 16,815 psi.
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5.3.5
NozzlePRO
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This compares very favorably to the Pl+Pb+Q+F value found in the NozzlePRO run of 15,487 psi. (especially when one considers that the reduction from 1.35 to 1.1 for the SCF for radiusing welds.) This model can be turned into a brick model by clicking the brick radio button on the Axisymetric Model Data . The resulting brick model results are shown below:
form:
The difference between the brick model results and the 2d axisymetric results is that the default model for bricks uses two elements through the thickness, where the default model for a 2d axisymetric analysis uses six – eight noded elements through the thickness. The plots below illustrate the difference:
2d Axisymetrc Default Mesh
Brick Default Mesh
The brick model can certainly be improved using the mesh multiplier, but run times increase significantly as the model size increases. Users should simply be aware of the differences and adjust their engineering evaluation accordingly. Turning OFF stress averaging for brick models will improve this condition. Overturning Moments on Skirts: The outside diameter of the vessel and skirt is 60 inches. The skirt is 0.75 inches thick and the vessel is (2) inches thick. The total design weight of the vessel is 64,000 lb. The horizontal “g” load from IBC 2000 is 0.62. The center of gravity of the vessel is 25 feet above the tangent line. Five feet of the vessel above the tangent line will be modeled, so the overturning moment at the section of the vessel five feet above the tangent line will be: (64,000)(0.62)(25-5) = 739,600 ft.lb. Copyright (c) 2007 by Paulin Research Group
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The shear load at this section will be: (64,000)(0.62) = 39,680 lb. There will not be a nozzle included in the bottom head. The main form input for this problem is shown below. The 10” nozzle dimension is entered because a valid nozzle OD and wall thickness are required inputs on this screen.
In the Optional Data form ask for axisymetric heads and skirts:
Click on Bottom Head Only, Include Skirt, No Nozzle, Brick Half-Model, and then Skirt Data.
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5.3.7
NozzlePRO
Fill in the skirt data screen as shown below. Note that there are numerous of geometry.
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buttons to help with interpretation
5.3.8
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The loads are entered on the Overturning Moment Data Form and the model can be plotted:
The stress intensities due to this load are shown below in plots from the 3d viewer.
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5.3.9
NozzlePRO
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5.3.10
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Chapter 5 – Section 4 Skewed Structural Supports in NozzlePRO. To skew a structural support, start with a regular support. A typical “T” type structural attachment is shown below:
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When the graphic window is displayed the user can select Settings:Stamps to get the following dialog box:
When “Plate Points” is checked the points used by NozzlePRO and FE/Pipe are shown on the plot:
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5.4.2
NozzlePRO
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The first step will be to shift the points on the end of the T section in the “t” direction 7 inches. This will be the points 7, 8, 9 and 11. There is no facility in NozzlePRO to do this so the FE/Pipe editor will need to be used. In the optional form the user would set the “Use FE/Pipe Editor During Run” checkbox as shown below. Note that the “Leave Data Files” box is checked automatically. This is so that files edited by the user can be reused. (Once we’re happy with our changes we don’t want to have to continue remaking them.)
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When the FE Run is started the following FE/Pipe screen is displayed:
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The 7-Plate Geometry option should be selected:
“Plate Points” should be selected from this screen.
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5.4.5
NozzlePRO
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As can be seen in the bottom right-hand corner there are 15 plate point screens. (There are 15 points possible for the variety of structural cross sections available in NozzlePRO.) The PageUp and PageDn key moves between the different screens. Page down until the first point that should be moved is shown. This is point 7:
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5.4.6
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Note that point 7 has a “status” of 3 – it is removed from the surface as might be expected. The “?” key can be used when the cursor is in any of the data cells to get help for the particular cell. Since the end points should be shifted from their current positions by 7 inches in the “t” local direction the input for points, 7,8,9 and 11 will be changed as shown below:
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These changes produce the skewed structural support shown below:
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5.4.8
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Using the changes in the r, s and t directions user’s can typically skew any NozzlePRO support in any manner needed. Since the movement of points is usually a trial and error procedure, we want to be able to do two things: 1) Go thru the change-plate point-plot procedure iteratively until the desired model is obtained. 2) Reuse the existing geometry once it is available. At some point using the NOZZLE.IFU file produced by NozzlePRO will be easier than going through the NozzlePRO backdoor to make changes to the FE/Pipe model. The user will have to decide how to best proceed on a problem-by-problem basis. Using NozzlePRO for structural supports is convenient because NozzlePRO distributes moments and shears over the structural attachment in a manner consistent with load distribution through structural section shapes. Without this load distribution procedure flanges might end up carrying vertical shear loads that they will not typically support and high, unreasonable stresses will result. Anyway, it is for the user to decide which is the best way to proceed once he is aware of the available options. The control of the input files occurs through the optional screen:
The last checkbox is the critical one. If left unchecked, whenever the NozzlePRO user requests a “plot” or an “FERun” NozzlePRO will overwrite any existing input file with the current data. If checked, then whenever the NozzlePRO user requests a “plot” or an “FE-Run” the existing FE/Pipe input file is used and the current NozzlePRO input is ignored. Using these options the user can make changes to thicknesses for example, and rerun the model without having to go through the model alteration process. If the user wants to change the loads on a structural attachment however, he can either change them in the FE/Pipe input if comfortable with this, or must go back to NozzlePRO to make the changes. In this case the FE/Pipe file must be overwritten with the new loads – and any geometry changes will have to be reentered. We generally go to this much trouble for two reasons: 1) We want to use the NozzlePRO load distribution algorithms. 2) We want the output in a NozzlePRO format. At any point FE/Pipe can be used with the NOZZLE.IFU input file produced, but the user must be somewhat familiar with FE/Pipe to get the reports and graphics that come automatically from NozzlePRO. User’s should find however, that once the changes that have to be made to a geometry are known, that remaking them after a load change is not such a big problem. This approach can also be used to add multiple nozzles or supports to a NozzlePRO geometry but support for this is not considered part of the standard NozzlePRO capability, and only FE/Pipe users should attempt these more significant modifications. A more meaningful example will be shown below:
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5.4.9
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The model will be similar to the one shown above. The load will be carried through the bolt section. Since flanges don’t transmit vertical load in the persence of webs, the load will be carried through the web section at the bolthole section. This is demonstrated below:
The 14” length of the starting orientation was chosen arbitrarily. Once chosen however it is a significant number since the points 7,8,9 and 11 will have to be moved from the end of the 14” section to the location where we want them. The point 9 will move from the (r,s,t) coordinate: (5,14,5.66) to the (r,s,t) coordinate: (5,4sin(45),4sin(45)+11.313/2) = (5,2.828, 8.485), the point 8 will move from the (r,s,t) coordinate (5, 14, 0) to the (r,s,t) coordinate (5,8sin(45),8sin(45)) = (5,5.657, 5.657). The point 7 will move from the (r,s,t) coordinate (5,14,-11.313/2) to the (r,s,t) coordinate (5, 12sin(45),12(sin45)-11.313/2) = (5,8.485, 2.83). The point 11 is below
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5.4.10
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point 8 will be moved from an (r,s,t) coordinate of (-5, 14,0) to (0,8sin(45),8sin(45)) This will put node 11 on the centerline in the vertical direction and will create the proper shear area at the bolt centerline section. The original input for this model in NozzlePRO is shown below:
The plot with Settings:Stamps:Plate Pts is given below: (Remember to check the box to use the FE/Pipe data editor so that plots can be generated from the changed geometry.)
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5.4.11
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The original plate point 9 is shown below:
The new point 9 location will just be typed over the original location. (The change from one to the other could be entered. The user should input whatever seems easiest for him.)
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5.4.12
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The support is shown below:
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5.4.13
NozzlePRO
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5.4.14
NozzlePRO
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Chapter 6 – Section 1 WRC Comparisons In general WRC 107 comparisons to FE/Pipe results are excellent when thin shells are analyzed and when the model is within the accepted parameters of WRC 107. Nozzles in the centers of heads are evaluated most accurately. Most WRC107 programs give the stress intensity at four points around the nozzle on both the inside and outside of the geometry. This stress is usually compared to 3Sm and is caused by all operating loads on the nozzle. The resulting stresses from a WRC 107 run of this type should be compared to the Pl+Pb+Q stresses from the finite element calculation. Note that Pl stresses evaluated in accordance with ASME Section VIII Division 2 are membrane stresses. These are the average stresses through the thickness and do not include the bending stress component at the junction. (See ASME Section VIII Division 2 Appendix 4 Table 4-120.1.) WRC 297 comparisons in the vessel or header tend to be good but become overly conservative when the high stress moves into the branch when the t/T ratio becomes less than 1.0. This result is certainly demonstrated in the finite element calculation. WRC 107 tends to be somewhat less conservative than finite element results, but that WRC 107 results parallel FE calculations through d/D ranges of 0.1 to 0.8, where the WRC and Finite element curves cross, the WRC 107 results becoming much more conservative beyond this range. (When the approach used outside of WRC curve parameters is “last curve value.”) The following list summarizes areas where WRC 107 ad WRC 297 are considered weak, or where further concern should be displayed: a) b) c) d) e) f) g) h) i) j)
d/D > 0.5 t/T < 1.0 Pad reinforced nozzles Hillsides or laterals Area replacement rules for pressure are barely satisfied and large D/T. Temperatures are approaching the creep regime. Cycles are greater than 5000. Design and operating conditions are approximately the same. The load consists of high-pressure stresses and high loads. The Piping attached to the nozzle is long, flexible, and somewhat unrestrained.
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Chapter 6 – Section 2 Engineering Considerations High Temperature – These are temperatures in the creep range for the material – usually in the 700 –to- 850 deg. F range and higher. ASME Section VIII Division 2 does not directly address creep range applications, and so actual calculations have been left to the interpretation of the user. It is suggested that users in these high temperature regimes enter ASME Section VIII Division 1 allowables. (Division 2 does not give allowables for these temperatures.) Nuclear Code Case N253 can also be used to compute a high temperature fatigue limit for Pl+Pb+Q+F stresses. What the Code Inspector Sees – Since the use of finite elements as a regular design tool is fairly new, Code inspectors vary in what they expect to see with regards to an analysis. In general, a cover letter followed by the listed tabular reports and color prints of the plotted results has been enough to satisfy most Code inspectors. The cover letter usually states that the included reports have been reviewed by a registered professional engineer and were found to satisfy the necessary Code section requirements for stress. In general, an inspector wants to be able to look at the input listing and see the correct allowable stresses, diameters, wall thicknesses and pressures. It is expected that some guidelines will be published in the near future that give the inspector additional guidance, and that give the user more freedom in pursuing less conservative designs. External Pressure – Where external loads and external pressure act simultaneously on a large or thin-walled opening, elastic instability may be of concern. The standardly applied ASME Section VIII Division 2 Code rules do not explicitly address elastic instability. There are nonlinear approaches available within the full version of FE/Pipe to deal with this problem should it arise. FE/Pipe can be started with the NOZZLE.IFU file described above, and an elastic instability (elastic buckling) calculation performed on the geometry to be sure that buckling load factors exceed the Codes intended buckling safety factor of 3. Elastic instability load factors for pressure vessel and piping geometries usually exceed 10. When the calculated load factors are in the 4-to-5 range extra care is warranted because non-simulated events such as wind gusts, frictional sliding transients, etc. can induce momentary overloads that result in the initiation of catastrophic buckling. Orthotropic Materials – The orthotropic material model has not been installed in NozzlePRO but is available in the full version of FE/Pipe. Pressure Stiffened Shells - Basketball, football and soccer players are familiar with the significant stiffening effects of even relatively low pressures on thin, membranes. This effect is also seen in the pressure stiffening of shell membranes used in piping and vessel systems. The effect tends to be more pronounced in plastic systems, but Rodabaugh suggests that “design pressures might reduce the flexibility by about a factor of 3 for out-of-plane moment and thrust loads and by about half that much (1.2 to 1.5) for in-plane moments.) The effect of pressure stiffening is a nonlinear effect included in the full version of FE/Pipe, but not available in NozzlePRO. Factors of Safety – Whereas the ASME Code rules are based on experience and tested results, the intention is to provide a consistent factor of safety for the varieties of different vessel and piping systems designed. In general, the factor of safety against fatigue cracking is two on stress. This means that in a perfect world, if the Pl+Pb+Q+F stress is equal to the allowable the component would fail at the end of its design cycle life at “twice” that stress level. The factor of safety against gross collapse or distortion is about 4 or greater. This means that in a perfect world, if the Pl stress is equal to the allowable the component would suffer a pressure boundary failure (burst), at somewhere between 4 –to- 8 times the load that caused that stress. Flanged Ends – For larger d/D and d/t ratios it is known that the l/d ratio and the rigid end stiffnesses can affect pressure stresses in the junction (l is the length of the branch). The 3D shell cylinder-to-cylinder models used in NozzlePRO attempt to put what is essentially an infinitely long pipe on the end of the cylinder-to-cylinder branch connection by default. Flanges are almost always stiffer than pipe, however, bolt loads and rotations of blinds can result in greater stresses at the shell intersection. Detrimental effects due to this condition may result in noticeable plastic deformation during hydrotest or in a leaking joint. Blind and matching flanged end nozzles are provided in the axisymmetric 2D and brick model options. The user is encouraged to investigate this effect further using these tools.
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Chapter 6 – Section 3 Finite Element Philosophies, Element Types, Etc. Standard Element Type – The basic element used in NozzlePRO is the eight-noded reduced integration curved shell element. While more difficult to formulate and solve using active column techniques, and subject to several inconsistent deformation modes, the element nevertheless has been found to be remarkably insensitive to shape and less sensitive to size than many of the more “formally” derived element types. Stiffness convergence is good even with the crudest mesh and non-averaged stress calculations give a good visual indication of the adequacy of the stress state. The element is basically the same curved shell element used in the Ansys program as STIF93. The formulation can be found in many finite element texts, one being:“Concepts and Applications of Finite Element Analysis,” by Cook, Malkus, and Plesha, 3rd ed., John Wiley & Sons. Special formulations are provided for transferring six degree-of-freedom piping-type forces and moments into shell models to prevent inadvertent local transfer of torsional moments into the shell. Adjustments are also made to the element Jacobian if needed to properly condition poorly shaped elements.
Stress Concentration Factors – Default stress concentration factors are used at as-welded joint locations for peak stress evaluations to bring the calculated shell stresses inline with observed fatigue test results. This approach has been used for over nine years at PRG in Houston. The only stress classification affected by the stress concentration is Pl+Pb+Q+F. The membrane stress Pl, and the secondary stress Pl+Pb+Q+F is the stress intensity calculated directly by the shell finite element procedure evaluated using the ASME Section VIII Division 2 tensor combination directions.
High temperature considerations, pressure stiffening, orthotropic materials, and elastic instability (buckling) are discussed under the topic “Other Engineering Considerations.”
Mesh Density – While every effort has been made to produce dependable meshes and gradients based on the variety of geometries there will be some configurations that will not be adequately meshed. It remains to the user to review the displayed stress patterns and to determine if these errant conditions exist, but in the majority of cases, “if the stress distribution looks reasonable,” the values are correct. New algorithms are being designed that will further improve the mesh quality and that should produce dependable solutions in a wider variety of situations. Extreme geometries will tend to produce the more difficult meshes. For example, a straight nozzle in the center of an elliptical head will be meshed correctly every time, whereas a pad reinforced nozzle on the knuckle of a dished head may have greater difficulties. The program will at times adjust pad and/or nozzle dimensions and locations to improve the quality of a mesh at the expense of model geometric accuracy. In these cases messages are printed in the Input Data report that should be reviewed. If the user is ever concerned that an adjustment made by the modeler produces a significant change in the solution results he is encouraged to vary the parameter himself in subsequent runs to assure himself that any changes or assumptions made by the program are inconsequential to the overall high stress behavior.
Element Sizes at Discontinuities – Element sizes near discontinuities of importance are influenced both by major geometric dimensions, the square root of RT, the anticipated stress decay, and by experience in running multiple similar geometries. Should the user think that mesh refinement or mesh “alteration” is essential for a particular problem the analyst may follow the “How to Get Help” procedure and submit the geometry for developer review. (See the section: “How to Get Help.”)
Shell Models vs 3D Models – Axisymmetric 2d and brick models of head and skirt geometries were added in Version 4.0 of NozzlePRO. The axisymmetric quad element is eight-noded, including four midside nodes along with the four corner nodes. The brick element used is the eight-noded brick element with extra shape functions to permit bending modes. Stress tensor components are extrapolated from the gauss points to the node points for plotting and tabular results. The axisymmetric 2d and brick elements were added primarily to: Copyright (c) 2007 by Paulin Research Group
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1) Allow users to verify shell models of the same geometry. 2) Permit a more accurate analysis of thick-walled intersections 3) Analyze geometries not directly amenable to shell solutions, such as non-integral repads and overturning moments on skirts. 4) More accurately calculated cyclic pressure stresses in thick-walled geometries. 5) Address basic steady state and transient heat transfer and stress problems. The user is strongly encouraged to compare the results from different model types. A center nozzle in a head subject to pressure only loads can be changed from a shell model to an axisymmetric 2d model by a single mouse click. Comparing these results can be quite informative.
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6.3.2