Relief Valve exemption on a PV ?
Relief Valve exemption on a PV ?
(OP)
Hi All,
I currently doing some inspection on some small pressure vessels that store air for the purposes of failing open/close control valves. So these are low pressure (less than 200 psig) and low temperature (near ambient temp) - they're also less than 5 ft high. While doing visual inspection, I noticed that some of the vessels have a relief valve whilst others don't. Looking up the drawings on the ones that don't, the drawing crossed out all the vessel connections which included one for a Relief Valve and it has an ASME stamp.
I looked up from the code and saw this:
Now all there is to the vessel is a tubing carrying air to it. That's it. No rupture disk or anything pressure relieving.
Now since it is from an Instrument air compressor whose discharge pressure is less than the MAWP (max is about 120 psig on a good day) would this lack of relief valve be allowed ? (there would be at least one RV on the compressor discharge line).
The reason I find this odd is that if it were by system design then none of the vessels would have RVs yet the majority of them do.
I currently doing some inspection on some small pressure vessels that store air for the purposes of failing open/close control valves. So these are low pressure (less than 200 psig) and low temperature (near ambient temp) - they're also less than 5 ft high. While doing visual inspection, I noticed that some of the vessels have a relief valve whilst others don't. Looking up the drawings on the ones that don't, the drawing crossed out all the vessel connections which included one for a Relief Valve and it has an ASME stamp.
I looked up from the code and saw this:
Quote (ASME BPVC UG-125(a))
(a) Other than unfired steam boilers, all pressure vessels within the scope of this Division, irrespective of size
or pressure, shall be provided with overpressure protection in accordance with the requirements of UG-125
through UG-138, or with overpressure protection by system design in accordance with the requirements of
UG-140, or a combination of the two.
Now all there is to the vessel is a tubing carrying air to it. That's it. No rupture disk or anything pressure relieving.
Quote (ASME BPVC UG-140)
UG-140 OVERPRESSURE PROTECTION BY
SYSTEM DESIGN
(a) A pressure vessel does not require a pressure relief
device if the pressure is self‐limiting (e.g., the maximum
discharge pressure of a pump or compressor), and this
pressure is less than or equal to the MAWP of the vessel
at the coincident temperature and the following conditions are met
Now since it is from an Instrument air compressor whose discharge pressure is less than the MAWP (max is about 120 psig on a good day) would this lack of relief valve be allowed ? (there would be at least one RV on the compressor discharge line).
The reason I find this odd is that if it were by system design then none of the vessels would have RVs yet the majority of them do.





RE: Relief Valve exemption on a PV ?
In many instances, local regulations require pressure relief valve to be installed on a pressure vessel, irrespective of the fact that there are no credible causes for process overpressure.
Dejan IVANOVIC
Process Engineer, MSChE
RE: Relief Valve exemption on a PV ?
Well I found this in the local law which we are "supposed" to follow.
RE: Relief Valve exemption on a PV ?
RE: Relief Valve exemption on a PV ?
RE: Relief Valve exemption on a PV ?
Apart from that, there is one RV on the entire instrument air header right off the discharge of the compressor.
RE: Relief Valve exemption on a PV ?
"...when logic, and proportion, have fallen, sloppy dead..." Grace Slick
RE: Relief Valve exemption on a PV ?
I don't think these PVs fit any of the exemption criteria and some of these are located in close proximity to both low and medium pressure steam piping so if there is a leak in the area, I can see there being a possible overpressure scenario assuming there is steam directly hitting the air receivers.
The IA compressor in my case would pressure a large air receiver which has an RV on it which then feeds the header and then to the PVs in question. So UG-140 here may work however I can't understand why the majority of PVs would have the RV unless that is just based on the manufacturer.
RE: Relief Valve exemption on a PV ?
General Blr. CA,USA
RE: Relief Valve exemption on a PV ?