Hydrotest pressure 1

[Jmoore1]

I have an issue with HT pressure for my piping system.... B31.3Code says to reduce hydrotest below Syt or 1.5 MAWP when the stress due to hydro will be greater than the yield stress of the pipe....

Now my hydrotest pressure brings me within 2000 psi of the yield stress of the material, and 1.5 MAWP is even greater than that, my questions is even though B31.3 says that you lower the test pressure below yield strength, can we actually come that close to the yield strength of the material (although its 2000 psi it is only ~6% off of yield strength), a simple stress concentration at a reducer or weld could easily pass this limit and we would never know the pipe was yielded until later????

 

[zdas04]

Every company I've ever worked for has a max hoop stress that is a (small) percentage of SMYS for MAWP (20-50% is pretty common). So if you set your MAWP at 50% of SMYS then a 150% hydrotest doesn't come close to yield stress.

David

 

[rcchap]

What is your design pressure and temperature, and pipe material, size, and schedule? What is the test temperature? Do you have expansion joints or other components in the system with lower ratings that could be exceeded?

Your statement that the hydro test pressure brings you to within 2000 psi of yield, and 1.5 times design pressure is greater than that .... doesn't make sense. B31.3 hydro pressure will be 1.5 times design pressure, and if the design temp is greater than the test temp, hydro pressure could be even greater than 1.5 times design pressure per Para 345.4.2. How did you determine a hydro test pressure that is less than 1.5 times design pressure?

Ultimately, I would be more concerned about the piping being designed with so little margin than about the possibility of a local stress concentration during a 10 minute test. Pipe is cheap ... leakage and ruptures are not.

I am assuming by MAWP you mean design pressure. I don't think the term MAWP is used in B31.3. MAWP is used in Section VIII.

 

[ione]

Jmoore1,

Take a look at the thread below which gives valid input when dealing with hydrotest limitations

http://www.eng-tips.com/viewthread.cfm?qid=274642&page=10

 

[Jmoore1]

Thanks Ione....same issue that I was having about the concern of a safety factor in the pipe....at hydrotest pressure of 1.5*design*temperature correction my minimum hydrotest was 1660, which exceeded my allowable stress and my MAWP. Seems that the safety factor is in there already.