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Join Date: Jul 2017
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Pipe Stress Analysis For Hydro-static Test Condition

07/26/2017 1:34 AM

I got a little confusion during the stress analysis of a gas line (my first experience of stress analysis) with ASTM A-106 gr. B pipe. We know that allowable stress for A-106 Gr. B pipe is 20000 psi as per Table A-1 of B31.3. But when i generated the report it is showing that allowable stress is 35000 psi for hydro-static load case WW+HP (marked in below image). Why is it so? Is there any clause in ASME B31.3 regarding this? Can anyone clarify this? Any reference will be appreciated. Thanks in advance.

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Pathfinder Tags: hydrostatic piping stress
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#1

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 2:27 AM

The required test pressure (and matching stress) is always more than the allowable working pressure (and matching stress). By how much may depend on local regulations and/or software authors.

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#2
In reply to #1

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 2:45 AM

Yes Tornado, Test pressure is 1.5 times the design pressure. Does the same implies to allowable stress for test condition?

We are taking about ASME B31.3 here. Can you please refer me to the clause in B31.3 regarding this increment in allowable stress for test condition?

thanks.

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#3
In reply to #1

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 2:52 AM

...and on material condition, which deteriorates with time, and is the considered and experienced view of the Engineer/Surveyor from the insurance company that is witnessing the test.

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#4
In reply to #3

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 3:14 AM

How often do they do retests on pressure vessels in your neck of the woods?

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#5
In reply to #4

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 3:17 AM

On locomotive boilers, every 10 years.

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#6

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 3:26 AM

I'm not so familiar with the ASME code but under API 6A the test pressure is 1.5 times working pressure but the allowable stress is not 1.5 times stress at working pressure. Allowable stress is 2/3 yield stress for working pressure but for test pressure it is 5/6 yield.

There is a column marked code stress, does this apply to ASME code? Not sure why it would be different for each node. But the column for allowable stress is 35ksi which is the yield stress of your ASTM A-106 pipe. Is the program just telling you that allowable is up to yield?

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#7

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 3:56 AM

"1 These bases are the same as those for BPV Code, Section VIII, Division 2, given in Section II, Part D. Stress values in B31.3, Appen- dix A, at temperatures below the creep range generally are the same as those listed in Section II, Part D, Tables 2A and 2B, and in Table 3 for bolting, corresponding to those bases. They have been adjusted as necessary to exclude casting quality factors and longitudinal weld joint quality factors. Stress values at tempera- tures in the creep range generally are the same as those in Section II, Part D, Tables 1A and 1B, corresponding to the bases for section VIII, Division 1. Stress values for temperatures above those for which values are listed in the BPV Code, and for materials not listed in the BPV Code, are based on those listed in Appendix A of the 1966 Edition of ASA B31.3. Such values will be revised when reliable mechanical property data for elevated temperatures and/ or for additional materials become available to the Committee."

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#8

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 6:45 AM

It is worrying that someone doing stress analysis for gas pipelines deems it appropriate to use an international Engineering forum as a reference rather than the standards, codes and procedures that are applicable to the project by the host Engineering organisation. Whatever is the world coming to (rhetorical question - NNTR)?

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#9
In reply to #8

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 10:28 AM

"Whatever is the world coming to" ......????!!!

It is coming to the current living hell with millions and millions of non-technical MBAs assigning work to newbie people who have never done engineering before ...... There are no senior engineering staff offering help, guidance and instruction to the newbies .... they have all been discharged.

Then somewhere, in some part of the world, a boiler or gas pipeline or refinery explodes ....

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#10
In reply to #9

Re: Pipe Stress analysis for Hydrostatic test condition

07/26/2017 11:47 AM

Amen...

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#11

Re: Pipe Stress Analysis For Hydro-static Test Condition

07/28/2017 4:59 PM

My guess is someone got assigned to perform a regulatory test required under 49 CFR 192 subpart J (under Department of Transportation, Common Carrier regulations). There are miles of pipeline that companies have installed as "customer service lines" that get triggered for certification when the company lacks specific expertise, so the new guy in the office gets a copy of the regs and little more.

Falls under that job description of "Other duties as assigned", I would venture.

If I seem to speak from experience, it was a LONG time ago!

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