PSV Set Pressure 10% Above Piping MAP?
PSV Set Pressure 10% Above Piping MAP?
(OP)
Hello,
I seem to remember reading somewhere that PSVs may be set 10% above piping MAP, as ASME B31.1 allows up to 20% overpressure of flanged piping for short durations. Has anyone else read this somewhere or did I just imagine this? Anyone have a code reference on this?
I am interested in raising the PSV set pressure to 10% above the 150# flange rating as the PSV often operates at 95-99% of PSV set pressure.
I seem to remember reading somewhere that PSVs may be set 10% above piping MAP, as ASME B31.1 allows up to 20% overpressure of flanged piping for short durations. Has anyone else read this somewhere or did I just imagine this? Anyone have a code reference on this?
I am interested in raising the PSV set pressure to 10% above the 150# flange rating as the PSV often operates at 95-99% of PSV set pressure.





RE: PSV Set Pressure 10% Above Piping MAP?
The relieving pressure can be as high as 133% of the piping design pressure, provided you don't exceed the hours limitation (no more than 10 hrs per incident and no more than 100 hrs/yr). (Ref: B31.3 paragraph 302.2.4)
Common question: Is the 33% accumulation allowance (paragraph 302.2.4) applicable to pressure relief events?
Answer: Yes, as long as the allowable hours are not exceeded. This is stated in an ASME B31.3 interpretation (Ref: ASME B31.3 Interpretation: 20-51).
RE: PSV Set Pressure 10% Above Piping MAP?
The fact that this PSV is triggered at MAWP " often " wouldnt permit the justification for this exceedence.