PSV Failing in Service @ Lower than Set Pressure

[octane]

A PSV repeatedly passes bench testing but lifts below set pressure in service.
That is not happening for the first time. 3rd instance as I recall.
What mechanisms should we investigate?

[mechcolor]

If a PSV repeatedly passes bench testing yet opens below set pressure in service, the problem is often not the PSV calibration itself but something in the installed operating environment.
For a third recurring occurrence, I would investigate the following systematically:
1. Built-Up Back Pressure
A conventional PSV is very sensitive to back pressure.
Check:
Is discharge routed to flare?
Has flare header pressure increased over time?
Are there simultaneous relieving events?
Any liquid accumulation in discharge piping?
Any plugged flare KO drum internals?
Symptoms:
PSV lifts early in service
Bench test shows normal set pressure
Issue appears only when installed
Rule of thumb:
Conventional PSV: back pressure can significantly reduce set pressure.
Balanced bellows PSV: less affected but still susceptible if bellows damaged.

[irish]

For a PSV that has now shown this behavior three times. You must focus on gathering actual lift data like date /time of each lift, process conditions, flare header pressure (if connected to flare).
Trend simultaneously the PSV inlet pressure, flare header pressure, compressor /pump status, control valve position.
Calculate superimposed back pressire, built-up back pressure, inlet line pressure drop and then inspect removed PSV for chatter marks, seat fretting, bellows condition, guide deposits, and vibration damage.

[octane]

That is exactly what we have been doing at the moment.
A formal incident investigation has been called to look into the causes and come up with recommendations.
Keep sharing your leads - thanks.

For a PSV that has now shown this behavior three times. You must focus on gathering actual lift data like date /time of each lift, process conditions, flare header pressure (if connected to flare).
Trend simultaneously the PSV inlet pressure, flare header pressure, compressor /pump status, control valve position.
Calculate superimposed back pressire, built-up back pressure, inlet line pressure drop and then inspect removed PSV for chatter marks, seat fretting, bellows condition, guide deposits, and vibration damage.

[ben]

Have you checked for some sort of vibrations where you install PSV?
Did you check if there are any transportation issues particularly with this piece when carried to the site?
Same technician, inspector are certifying this piece every time that is tested in the shops?
Did it actually pop at the right test pressure once reported lifting at low pressure at site?

A PSV repeatedly passes bench testing but lifts below set pressure in service.
That is not happening for the first time. 3rd instance as I recall.
What mechanisms should we investigate?

[octane]

We have checked the vibrations - negative.
Transportation issues - not any we could know.
Same team inspecting and certifying- no, a different technician and inspector involved each time.
Once received at workshop after reported lifting at lower pressure, it failed the bench test as well.