Pop test of relief valves
Pop test of relief valves
(OP)
Hi all,
We have problems with the performance of relief valves on site, the valves when taken to test bench in " as received" conition for pop test , they generally do not lift on the cold diff set pressure (within the tolerance) which then reduces the next run campaign of the relief valves. AS per contractor spec for pop test of valves , the max pressure applied to the valves are 10% in excess of the CDSP or cold diff set pressure, if the valve doesnt found to be lifted, no pressure is applied considering it unsafe ( as you are going over the design pressure) this is considered as valve sitting on "high" . API 576 does allow to increase the pop pressure to 1.5 times if the valve doesnt not lift at first instance. This is done to ensure that valve seat gets released of found stuck.
My question is around inceasing the test pressure to 1.5 times the CDSP, how do you justify increasing the pressure to 1.5 times the design pressure (or CDSP) Secondly I would like to have the comments from other uers if they have had similar experience with pop test.
We have problems with the performance of relief valves on site, the valves when taken to test bench in " as received" conition for pop test , they generally do not lift on the cold diff set pressure (within the tolerance) which then reduces the next run campaign of the relief valves. AS per contractor spec for pop test of valves , the max pressure applied to the valves are 10% in excess of the CDSP or cold diff set pressure, if the valve doesnt found to be lifted, no pressure is applied considering it unsafe ( as you are going over the design pressure) this is considered as valve sitting on "high" . API 576 does allow to increase the pop pressure to 1.5 times if the valve doesnt not lift at first instance. This is done to ensure that valve seat gets released of found stuck.
My question is around inceasing the test pressure to 1.5 times the CDSP, how do you justify increasing the pressure to 1.5 times the design pressure (or CDSP) Secondly I would like to have the comments from other uers if they have had similar experience with pop test.





RE: Pop test of relief valves
RE: Pop test of relief valves
RE: Pop test of relief valves
To have to go to 1.5x set pressure to get your PRV to 'Pop' means that the PRV is waaay out of calibration, jammed with deposits, or the spring is broken. And I agree that this is not acceptable. Your PRV's are being used too long between Test & Reset's. You might try a 2-port Full Port ball valve under 2 PRV's. That makes one 'live' and one valved-out at all times. Allows you to remove one PRV and clean & reset it mid-campaign. We do this with our ammonia-tank PRVs. Each PRV goes to Test & Reset every other year [send one PRV out each year], but the tanks stay in service for a decade.
RE: Pop test of relief valves
At the same time it is also true that 1.1 times the set pressure is also too low, normally we have plant run campaign of three years and so are the freqency of re-test with relief valves. In relief valves there are close tolerances within sleeve and stem which can get jammed due to rust, deposition of foreign particles, rust,, dust etc (more in cae of valves with no bellows), seat may get stuck with nozzle, only 10% overpressure may not be sufficient to lift the valve. The outcome of this exercise will not provide enopugh information for assessing the PSV condition required to determine its overhaul and re-test frequency.
RE: Pop test of relief valves
This is a perfectly reasonable bench testing procedure.
RE: Pop test of relief valves
That PRV needs more TLC - tender, loving care, and a shorter run interval.
RE: Pop test of relief valves
Now, some customers that we deal with use 10% overpressure! this is their own guide lines set by their inspectors which take into account over pressure for the piping and vessels.
API 576, is a guide line or recommended practice, at 1.5 times the set pressure this is to take into count the inlet flange rating of the valve as to not exceed the allowable working pressure of the PRD eg: 600# inlet flange set at 1440 psi at 1.5 = 2160 psi, the maximum test or hydro test pressure for the valves inlet, or primary pressure zone for the valve!
In the event that you want to find out what the valve is really doing, you can us this for investigation purposes, like, to find out if the valve has been set to incorrectly from a service company or if it is indeed a process problem!