6 years old problem of PSV leaking at a petrochemical plant 1

[Mous1747]

this has been a long standing problem of PSV leaking, the PSV is installed directly on a pump housing at discharge, the PSV has been leaking and get replaced every month or two on an average. the PSV never lifted, it just leaks. there was never a detailed RCA done on this but the recommendation was always to relocate the PSV on the piping downstream from the pump.

the set pressure is 3900 psi with backpressure of 300 psi (CDTP 3600 psi) the pump will trip at 3650
the PSV is metal seated with SS trim

the PSV manufacturer say it's overpressure or pressure pulsation because he is seeing severe damage to the disc and nozzle seats, but that can't be true if the valve is not even lifting?
also it's not chemical compatibility issue because SS should be okay with ammonia and will not corrode in a month.

it's a reciprocating plunger pump so maybe the pressure pulsation generated can cause this? especially that the PSV installed directly on the pump housing can cause misalignment inside the valve?

thank you all in advance, your inputs will be greatly appreciated.

 

[LittleInch]

Brand etc, I have no data - you would need to see an instrument company or specialist vibration analyst.

I would make it as close to the manifold as you can get.

Just try goggling high speed pressure transmitters. I know this one says discontinued, but similar exist.

https://www.omega.com/pptst/DPX101.html

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

 

[Mous1747]

I contacted OMEGA they have this transducer instead

https://www.omega.com/pptst/PX409-USBH.html

but the speed is 1 millisecond instead of the 1 microsecond , so basically it will read 1000 readings per second. i think that's an acceptable speed, correct?
i will not need oscilloscope in this case because the USB will connect directly to my laptop, right?
finally i will install the transducer as close as possible to the PSV inlet

 

[LittleInch]

I think that should catch your pressure spikes.

How you manage to catch the data is beyond my instrumentation knowledge... ~the website makes it look like you can do it with their software and laptop.

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

 

[Mous1747]

If I put a rupture disk under this PSV I would not need to change the set pressure? Because the valve inlet will be protected from pressure spikes ?

Just wondering if that could be a benefit of having RD under the PSV it will actually protect it from seeing the pressure spikes and i will not worry about premature leaks or simmering or any of these issues.

 

[PRVBoss]

What is the PRV protecting? Just the pump casing or the downstream equipment and piping too?

Consider setting it higher, if possible, based on the design pressure of the protected equipment. A pilot operated PRV would be a good solution as previously suggested. If a pilot is undesirable, would ensure you have a soft seat liquid trim PRV.

 

[Mous1747]

soft seat?why? i think metal seated would be better because the O-Ring would get damaged very easily when the seat is simmering at almost 4000 psi

that's why i was wondering if i put a rupture disk under this PSV i will eliminate this issue all together because the PSV will not see the pressure spikes so it will not be simmering and leaking all the time

 

[PRVBoss]

Soft seats are tight to 95% of set when >100 psig. Not as good as a pilot (~98%), but better than a metal seat and a decent option if your company avoids pilots (some operators just don't like them for various reasons). If the improved seat tightness eliminates the simmering then you're going to avoid the damage. First though, I would evaluate the design pressure of the system and the peak of the pressure spikes to maximize my set pressure while maintaining a safe system.

In a cyclic operation like yours, rupture disks can burst prematurely and below marked burst pressure due to fatigue so you might just be back in the same boat, but now replacing disks too.

Attached is a clipping from the 2002 Consolidated catalog (SRV-1/Q2.02, pp. 1900.12-1900.13) on soft seats and also Consolidated's recommendation for compressor discharge and PD pump application.