HYDROSTATIC TEST PRESSURE TOLERANCE

[roca]

I have seen in a client specification that the actual applied hydrostatic pressure for vessels shall not be exceeded by more than 3% for any reason.

I have never seen such a requirement before.

I know that in accordance with Code requirements test pressure gauges have to be calibrated before use.

Has anyone seen such a requirement before?

 

[JR97]

roca,

I also do not know of a Code hydrostatic test pressure tolerance. However, III-NB-3226 states if the pressure exceeds the required pressure by more than 6% then resulting stresses must be checked back to actual material properties.

I use the 6% as a rule of thumb when setting safety relief valves during hydrostatic tests and proceduralize the upper limit of test pressure at 3-5% above minimum pressure required by code. That usually gives a wide enough tolerance that the pump can be stopped without overpressurizing while allowing sufficient cushion above minimum to allow for settling.

JR97

 

[gr2vessels]

roca,
I believe that the 3% tolerance on the test pressure was only allowed by the Inspector witnessing the hydrotest, before aplying the crown stamp, in old days. It was also allowed a 3% excess on the yield, during the hydrotest, under strict deformation control. Once the hydrotest completed, the vessel has received a cold residual stress relieving process, mainly applicable to corrosive service, to the vessels made of Austenitic Stainless Steel. Interesting topic, I think I'll spend some time to see if is still applicable the "3%" or not these days.
cheers,
gr2vessels

 

[deanc]

What you have is an old requirement for SecI. It has changed see 2007 ASME Sec I, PG-99.1 and Sec VIII Div 1, UG-99 (d).

 

[decode]

It used to be a requirement of Section I, i need to check previous editions, but this is not currently in the 2007 edition.