Proof Pressure. What is it anyway? 1

[dacoach]

Is Proof Pressure a different test than a hydrostaic or pneumatic test for pressure vessel? What is it governed by with regards to testing requirements? 1.5 X MAWP or is it greater than that?

We bought an accumulator last year with the nameplate listing a MAWP of 3000psi and a proof pressure of 6000psi and a hydrostatic test rating of 4500 psi.

This year we are buying the same accumulator with a MAWP of 3000 but the proof pressure is said to be 4500 PSI (We haven't recieved it yet). Is their a std. with regards to proof pressure testing? Is it supposed to be 2X the MAWP? or can it be Lower or equal to say the hydrostatic test?

 

[doct9960]

dacoach,

Refer to UG-99, UG-100, and UG-101 of ASME VIII Div. 1.

Is your vessel a hydraulic accumulator?

 

[dacoach]

Yes it is a nitrogen over oil accumulator with floating piston. From what i am gathering from 1976-1989 proof test was synonomous with hydrostatic pressure test until ASME now defines it as a destructive test since it can cause deformation (i.e. burst test) so they don't want it used to refer to a hydro test.

Apparently hydro test to 1989 code year is 1.5 X MAWP and 1.3 X MAWP to 2004 code year but i guess you are also supposed to multiply some stress intensification factor ration to these to get your hydro test number..

 

[doct9960]

dacoach,

That factor you are referring to is in UG-99(b). It is the lowest ratio of the stress value for the test temperature to the stress value for the design temperature.

 

[AIAIAANI]

In Italy gas cylinders (forged) in accordance with national safety requirement were hydrostatic tested at 1.5 MAWP and one sample each lot (max 200 pcs)was required to be burst tested and bursting could not occur at less than twice the MAWP. I presume other european standard required the same. Now, with the PED (Pressure Equipment Directive), things have changed. Probably your accumulators show those two pressures. According to ASME not the hydrostatic, nor burst test pressures shall be stamped: your uncertainity demonstrate ASME are right. Don't argue about other pressures stamped: trust on MAWP only. Mauro