Featools Intro Webinar Scripted for Intergraph

8/12/2019 Featools Intro Webinar Scripted for Intergraph

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FEATools TM Ease and Benefit of Adding FEA Results to Piping and Pressure Vessel Designs

Presenter : Tony Paulin, P.E .


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There are certain well-known situations where present analysis techniques provideboth non-conservative and wildly over-conservative results.

Finite Element solutions , when properly tempered by comparisons with test data have

been shown to provide better answers for many of these cases.

Production pipe stress and pressure vessel design and analysis is usually a schedulesensitive activity. Delays, and changes can be expensive. Waiting weeks for acomplicated analysis can be expensive.

The objective is to use the latest technology, (whether its finite element based or not)to get the right answer with software that is familiar to the user and to keep theproject on track, cost-effective and safe.


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1-Dont say a line is overstressed and needs to be rerouted if it doesnt

2-Avoid adding loops if you dont need them

3-Dont build $50,000 supports for pumps that dont need extra support

4-Avoid cracking in heavily cyclic systems

5-Dont overestimate the stress by 8 times

There are practical implications!


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FEATools TM Summary:

1) Show common situations where FEATools (or other improved calculations)can significantly improve accuracy of results, production and workflow.

2) Look at some examples. (So we know when we should be careful.)

3) Look at how FEATools addresses these problems.

A balanced approach


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When we talk about well -known situations where present analysis techniques provide non-conservative results, we can start with B31.3:


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Piping Code Limitations:

D/T > 100 0.5 < d/D < 1.0 may be non-conservative.

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iob for t/T between 0 and 1.1


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iob for t/T between 1.1 and 100


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First recorded fatigue tests for piping recordedby Markl. Dynamic shaker tests conducted byBlaire between 1935 to 1945.

PRG k-factor, i-factor and I-factor testsconducted in 2013 Houston Tx.

Piping Fatigue Tests from 1935 to 2013


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Low Carbon Steel UFT (Sketch 2.3)GTAW Intersection WeldD/T = 91


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Model Deflection(in.)

Stiffness Difference(%)

No k-Factors 0.019 2631 lb/in. 69%

FEATool/CAESAR IIk-Factors

0.032 1562 lb/in. 0.5%

Measured 0.032 1553 lb/in.


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There are definitely warnings given to us as designers in the Codes, the (B31.3 AppendixD Notes for example), and there are definitely a few holes in the test data record.

In 1987 WRC 329 identified weaknesses in the Code that could be corrected. In the late

1980s ASME Section III implemented almost all of the WRC 329 recommendations inSections NC and ND. The B31 Codes have yet to incorporate those modifications, but the

ASME project ST-LLC 07-02 was written to provide a basis for extending the WRC 329recommendations, and later work by EPRI, WRC and others, to the B31 Codes.

Lets take a quick look at some of the notes in WRC 329 that are yet to be incorporated intothe B31 Codes


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20Short Header Long Branch Short Header Short Branch Long Header Long Branch


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WRC 329 p.22

d D < 1

Run SI s


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UnreinforcedTees

B16.9

WeldingTees

Out-of-plane Stress Intensification Factor (i-factor) for Two Tee Types


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Basically dont use the effective section modulus (Z e) withthe new set of equations...

AND Fix Weldon Fitting i-factors (Olets)


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?


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Mob comparison of test, B31.3 andST-LLC 07-02 for UFTs, EXTs, and Olets.

WRC 329 Fig. 16


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Markl emphasizes thatthe ratio (safety factor)between the designallowable stress and themean failure curve is two.

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WRC 107 and WRC 297 are commonly used tools.

WRC 107 cylinder-cylinder evaluations do not include the stresses in thenozzle which can be important when t/T < 1.

WRC 297 attempted to resolve the nozzle stress problem, but is overlyconservative as suggested in WRC 335:

PinholeExcavation

Pressure Vessels


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6 8


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From: PVP-61871


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What are the errors why didnt I see them in all my years working in pipe stress?


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WPW -WeldedWPS -Seamless


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User can select teefabrication style. Options arebased on measurements made

by Paulin Research Group

So far the discussion has centered on errors to be corrected:


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So far the discussion has centered on errors to be corrected: Missing k-factors for all branch connections Fig. 15 Moment/Stress error of about 9 Errant run side i-factors small d/D Tees Error 8 times too high Omitted torsional i-factor for tees Error equal to i o. (For large D/T ~ 10) Olet i-factors are off by 2. WRC 107 No stress in the nozzle t/T3125) The piping or vessel system operates in the creep range

Failures/cracks occur most often: Offshore where displacements and cycles can be large and high Any onshore batch process where cycles can be high Dynamic, high cycle situations Throttling conditions (high cycles) Pipe stress by proxy (let the software or the designer do the analysis)

When Loads are Important When stresses govern they may be off Rotating Equipment


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Summary: Calculation errors are generally a function of D/T Bigger errors exist as D/T > 50

When cycles > 3125 stresses should be accurate k-factors can affect loads which can affect

rotating equipment stresses (When stresses control FEAtools might be able to help.)

Short, stiff pipe accentuate the k-factor affect. (Is L less than kd?)

FEATools TM


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i-k Spreadsheet

FEATools TM


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WRC 329 Fig. 15 Example Piping Model


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Expecting: High k-factors for the branch Low k-factors for the run (d/D


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WRC 329 Fig. 15 Example Piping Model

Without considering the branchconnection flexibility of the 12x30

fabricated tee at point 15 the out-of-plane (Z) bending moment at point 15is 372,000 in.lb. Including the branchconnection flexibility reduces thebending moment to 41,832 in.lb., areduction of 8.8.


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Example No. 5 Heater Piping


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Example No. 5 Heater Piping


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Nozzle Load Analysis:

62 OD x 0.5 Thick

M = 35,287 ft.lb.(423,444 in.lb.)

14 OD x 0.375 Thick

Overstressed Add a 4x 0 375 pad


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OK With4 x 0 375 pad

62 OD x 0.5 Thick

M = 35,287 ft.lb.

(423,444 in.lb.)

14 OD x 0.375 Thick


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62 OD x 0.5 Thick

M = 35,287 ft.lb.

(423,444 in.lb.)

14 OD x 0.375 Thick

FEA Agrees that the Shell is OK but thenozzle neck is overstressed.


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Conclusions:


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1)If you have at least one copy of CAESAR or PVElite you should have at least one copy ofFEATools.

2)The PRGiK spreadsheet will give you a good sense of when the B31 i-factors and k-factorsmight be off compared to a variety of other methods. If all the other approaches give essentiallythe same i-factor and B31 does not agree with the i- factor, then its likely that all the otherapproaches provide more applicable data

3)FEATools does provide analysis of single FEA models for tees and bends with staunchionsincluded with the i-k spreadsheet and the CAESAR II model translator.

4) The FEATools translator will take one CAESAR II piping model and convert it into anotherCAESAR II piping model that incorporates all the FEA and i/k features discussed in thispresentation.

5)Some systems are more sensitive than others. You need to decide how much FEATools meansto your work. The PRGiK spreadsheet should give you some idea. Lots of straight pipe andelbows generally means little affect from intersection k- factors. Where theres only a littlestraight pipe and a few elbows the CAESAR II model translation can result in large differences inloads and stresses.

6)Affects are more significant when there are high D/T branch connections in the piping system.Results are more important when the number of cycles is greater than 3000 to 7000.


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Thank you for your time.

T. Paulin

Documents

Featools Intro Webinar Scripted for Intergraph