reason of PSV pop up agaisnt the set value

[Ayed99]

gentlmen.
how are u all
how to analyze the reason of psv poping up aginst the set vlaue. set value is 125kg/cm2 and it was pop up at 130kg/cm2.
is it normal or upnormal.
please advise

 

[Danlap]

Hi,

Its almost obvious that you only look for easy answer and don't do the research first:
a. Please find out how this forum works.
Use Safety Relief Valve engineering forum for PSV / SRV question.

http://www.eng-tips.com/threadminder.cfm?pid=1203

b. You can simply google what is Set Up pressure and Pop up pressure for PSV. Or find through this SRV forum
c. As engineers all related data must be specified. Type of PSV, medium, etc.?

There are 5 (simultaneous) phase that a standard PSV experienced. It happens in a blink of an eye:
- Opening pressure (droplets of liquid - noncontinuous)
- Set up pressure (continuous flow)
- Over-pressure (continuous flow, however with more speed). See drawing below
- Heavy flow (surge of flow)
- Gush / Pop up (the final surge and usually followed with loud banging)

Short answer of your question: Yes, it is normal.
How to analyze (in detail): your (PSV) process selection, NB (National Board) released specification of your selected valve, your (protected) Pressure vessel governing code.
A more senior PSV expert (me is not senior nor expert) may have different view.

Regards,
MR







Greenfield and Brownfield have one thing in common; Valve(s) is deemed to "run to fail" earlier shall compared to other equipments

 

[LittleInch]

Fully agree.

See what the valve vendor promised you. Standard spring reliefs are often something like -8, + 3% on set pressure.

Therefore your 5 kg/cm2 difference is fine, but as noted above, when testing, it is difficult to get continuous flow.

It does depend on your vendor and what type of valve you have.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[e43u8]

Ayed99,

It's in allowable tolerance range, +/-3%, of set pressure; then there would be no problem...

 

[niteshgargeck]

there can be several reason of it.
if psv outlet was connected to any header so may be because of increased back pressure itz popping up on highr pressure.
pop up pressure decided by spring force. check your maintenance history,was any adjustment done with spring in past.
is there any cdsp detail given in datasheet.

 

[MortenA]

Im not sure if I add any value, but

API 520 allows 10% overpressure with reference to the MAWP. So if your valve lifts above SP then it must still have the max capacity at 10% over pressure. For a spring loaded valve the 10% is to allow for the fact that the spring has to be "compressed" before a larger gap between the disc and the seal is opened allowing for a larger flow. Other PSV types e.g. piloted can open fully at the SP allowing for max flow at this (although flow will increaes up to 10% - but here its not due to the valve opening more and more just that a higher P increases the capacity. You should take a look at API 520 - especially fig 6 and 15.

 

[JAlton]

Regarding you question, the comment from e43u8 answers your inquiry. As a member of ASME Sub-Committee Safety Valve Requirements for 24 years and Vice Chair of NBIC Sub-Committee Pressure Relief Devices, and an NBIC VR Training Program Instructor from 1987 until 2015, I can tell you that the comments regarding the posted PRV Drawing on MAX Ovepressure are incorrect. I made that drawing for the NBIC VR Class. Now, here are my view of the comments above:
There are 5 (simultaneous) phase that a standard PSV experienced. It happens in a blink of an eye:
- Opening pressure (droplets of liquid - noncontinuous)
- Set up pressure (continuous flow)
- Over-pressure (continuous flow, however with more speed). See drawing below
- Heavy flow (surge of flow)
- Gush / Pop up (the final surge and usually followed with loud banging)
First; you cannot have simultaneous phases (the two words are antonyms).
Second; Opening Pressure is a Definition of Set Pressure, not drops of water.
Third; Set up pressure is incorrect terminology, it is just Set Pressure.
Fourth; Overpressure for Liquid Service is typically the point at which the PRV gushes.
Fifth; Heavy Flow is more than Opening Pressure (typically a steady stream dropping straight off the outlet), but less than the Gush.
Sixth; Gush is the point at which the PRV flows maximum capacity of Liquid, not Air/Steam/Gas/Vapor. The Loud Pop is Set Pressure. "Banging" implies repetition which indicates Chatter, which is abnormal and limits capacity.

JAC