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ASME B31.4 stress Calculation compatability of design factors

ASME B31.4 stress Calculation compatability of design factors

ASME B31.4 stress Calculation compatability of design factors

(OP)
Our specification requires design of a cross country steel water pipeline to AWWA, The designer is submitting designs to ASME B31.4. A standard which we are not familiar with in the water industry. Very helpful responses on the piping forum have warned of the dangers of mixing AWWA and ASME standards:

I would welcome any additional comments on the compatibility of the pipe stress design criteria proposed by the designer>

1) Hoop stress ASME B31.4 - 402.3.2 (a) -
 Sa = 0.5*E*S
(Standard allows 0.72 ??)

2) Additive longitudinal stress 402,3.2 (d)
Sa = 0.72*0.75*S

3) Expansion stress 402.3.2 (c)
Sa = 0.72*S

4) Effective Stress 402.3.2 (e)
sa = 0.9 *S

5) Occasional stress
Sa = 0.8 * S

Sa = allowable stress
S = minimum yield strength.

Maximum surge allowance 10% 0f working pressure
Test pressure 1.25 * working pressure.

It would appear to me that the  designer is reducing the hoop stress factor from the allowable 0.72 to 0.5 in order to comply with AWWA standard, but 1) is only allowing a 10% overstress for surge whereas AWWA would allow 50% and 2) is not reducing the allowable stress for other load conditions.

Am I getting a pipe that is substantially over designed in respect of working and transient pressures but under designed with respect to other loads and effective stress?

Do I need to buy myself a copy of B31.4?

RE: ASME B31.4 stress Calculation compatability of design factors

If you're going to use AWWA specification it seems very strange you let your designer persist with using B31.4.  I really don't understand that, but so be it.

Why not just use your designer's copy?  Or go ahead, buy your own copy.  If you let your designer design to B31.4, you probably need your own copy anyway.  Until you get it, the US Code of Federal Regulations, CFR, Title 49, Part 194 is the legal requirement for Pipelines carrying Hazardous liquids in the US and basically follows B31.4.  All CFRs are available online.  You might get a bit of a head start by reading Title 49, Part 192.

http://virtualpipeline.spaces.msn.com

RE: ASME B31.4 stress Calculation compatability of design factors

(OP)
Big-inch - thanks for your response. Contractually I have got a lot of backtracking to do to resolve this. some work has been approved to AWWA and some to ASME. The poject is in Libya and the designer is in Austria.

The on-line reference is just what I needed for bed time reading - cheers.  

RE: ASME B31.4 stress Calculation compatability of design factors

Now I "get it".  That particular design company is very accustomed to using ASME pipeline specs and would not normally use AWWA for anything.  I can very well image their resistance to AWWA.  It would probably involve a large cost of retraining their staff to move to AWWA for one project.  It also probably results in a more cost efficient design for your organization as well.

http://virtualpipeline.spaces.msn.com

RE: ASME B31.4 stress Calculation compatability of design factors

On second thought, drop me an e-mail.  Address in on my webspace page, contacts section.

http://virtualpipeline.spaces.msn.com

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