Over Pressure Allowance on Hydrotests??? 2

[Cuemaster64]

My construction testing crew inadvertantly let a test creep up over my stated test pressure due to an increase in temp on the line during the test and didn't bleed it down as they were supposed to. When my QC found the gauge it was @ 3500 kPa. Test limit supplied by Client was to be 2950 kPa. Piping materials are for a 150# flange rating with A333-6 pipe and A350-LF2 fittings (flanges). How do I assure the client that every part contained within the test will be okay? Client would like a detailed explanation and I am having trouble finding something within the B31.3 and B16.5 codes. What would you suggest I do in this situation? Any help would be appreciated?

Previous history at this site has had one other test go awry with the overpressure of a stainless line being effectively doubled and it was let go because of some engineers approval. I am not an engineer so I am not sure.

I hope this is enough info.

 

[zdas04]

I would calculate hoop stresses at the weakest component and see how close to SMYS you were. If that works out to something under 70% of SMYS I'd sign off on it. If you exceeded 70% of SMYS then you might want to inspect any component that had hoop stress that high for deformation.


David Simpson, PE
MuleShoe Engineering

http://www.muleshoe-eng.com

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

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[KernOily]

The hoop stress idea suggested by David would be a good start, for the pipe and fittings.

Did you test through any valves? Pretty tough to calculate a hoop stress in a cast or forged valve body. In that case, to do this rigorously you would have to run a FEM model of the valve body to see how close to Smys you got. This is Not a trivial task.

 

[Cuemaster64]

Thank You very much zdas04 and KernOily for your directions and advice. Upon further research I have found that the final SMYS number to be at 66.6%. This number I can explain to my Client but I am still at a loss as how to justify that number. Under B16.5 there is a reference to changing the 60% factor to 70% for groups 2 and 3 materials but I can not seem to find any concrete code or reference to quote.

Any suggestions??

 

[KernOily]

One thing you could do would be to see if you can get an AI from the client's carrier to sign off on it. Show him your hydrotest pressure chart and your calcs that you were at 66.6% of Smys and let him make the call. I'd think that would be good enough for anybody.