Can a Relief Valve Set Point be set higher than the MAWP
Can a Relief Valve Set Point be set higher than the MAWP
(OP)
I have a pressure vessel that has a U-1 form (as well as the nameplate) that has two different MAWPs and MDMTs.
One MAWP is 250 psi @ 300F and the other MAWP is 85 psi @ -50F. We operate this vessel between -30F and -40F. The vessel contains anhydrous ammonia and is operated at around 9"hg.
Questions:
Which MAWP do I set my RV's to? 250 psi or 85 psi or something else?
Can I operate the vessel at the conditions of -40F (with an MAWP assigned of 85 psi) with 250 psi RV?
If yes, where in ASME UG-125 does it permit this design?
I understand that manufacturers can provide additional MAWP and MDMTs, but how does an owner/operator comply? I have upload the U-1 form.
One MAWP is 250 psi @ 300F and the other MAWP is 85 psi @ -50F. We operate this vessel between -30F and -40F. The vessel contains anhydrous ammonia and is operated at around 9"hg.
Questions:
Which MAWP do I set my RV's to? 250 psi or 85 psi or something else?
Can I operate the vessel at the conditions of -40F (with an MAWP assigned of 85 psi) with 250 psi RV?
If yes, where in ASME UG-125 does it permit this design?
I understand that manufacturers can provide additional MAWP and MDMTs, but how does an owner/operator comply? I have upload the U-1 form.





RE: Can a Relief Valve Set Point be set higher than the MAWP
Try read the U-1 again;- it says MDMT is -20 F at 250 psi and -50 F at 85 psi.
That is, you can operate the vessel at 250 psi down to -20 F, but not at -30 - 40 F.
I believe you could interpolate to work out the MAWP at - 40 F and set your PRV at that pressure, not any higher than that.
Cheers,
gr2vessels
RE: Can a Relief Valve Set Point be set higher than the MAWP
As long as the vessel is operated within the temperatures of -20F to +300F, the MAWP is 250 psi and my RV can be set to 250 psi.
When the vessel is operated between -50F to -20F, the MAWP is 85 psi and it needs an RV with a set point no higher than 85 psi.
Am I am talking about true operating conditions, not upset scenarios where the vessel is seeing deviated conditions from the normal operating parameters.
Where am I wrong in this basic understanding?
RE: Can a Relief Valve Set Point be set higher than the MAWP
Cheers,
gr2vessels
RE: Can a Relief Valve Set Point be set higher than the MAWP