How to determine the Test medium to be used to test and set PSV's.

[Tectch84]

I am currently providing third party witnessing at a PSV shop that reconditions and adjust set pressures on PSV's, I am curious to know, how the test medium is determined from Air, Water, Steam. How can i find the specific gravity for say, C4 hydrocarbon or ethelyene or caustic, and how to determine the test medium to be used for each process. This may be a loaded question, but i would like to be pointed in the right code. Been through ASME VIII, PTC 25, ASTM D1298 and of course API 576, and 527.

 

[bljnv]

Air is used as medium of test for compressible services. The pop point on the test bench is corrected for service temp and back pressure conditions. This is called cold differential set pressure. For liquid service the test medium is water.

 

[Duwe6]

Your question actually has an easy answer: test fluid is based on the PRV's rated units. Thus
PRV's rated for "lb/hr" are for steam service and test with steam.
PRV's rated "scfm" are for vapor service, and test with air/nitrogen
PRV's rated in gpm are for incompressible flow and test with water.
You also need to be sure that the set-point is for the client's CDTP, if they specified one; not the in-service relieving pressure. The 'cold' part of CDTP gives the set-point at room temperature, thus what a shop test should yield.
NOTE: there is never a CDTP for lb/hr - being tested with steam, the shop test approximates the in-service condition.