Leaking PSVs 1

[Epoche]

Our company is doing a PSV audit for a client and they would like PSVs that are leaking to have size verification done. Is this necessary? I was wondering what other opinions are on this?

Thanks!

 

[chicopee]

Are you refering to relieving capacity at set pressure?

 

[LittleInch]

I might have an opinion if I could work out what you are talking about.

If a psv is leaking it either needs to be fixed or means you are very close to it's set point or has lifted and not reset properly.

Size or capacity has nothing to do with "leaking" so I just don't understand the issue.

What sort of audit is it?

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[Epoche]

I guess the best description of the audit is that it deals with safety. Such as making sure discharge piping is braced/supported, there are signs on discharge piping to warn workers if vented to atmosphere, checking that valves on the PSV piping are car-sealed open, etc. It is a visual inspection on the PSV's to make sure there are no safety deficiencies with them.

If we are to find a PSV that is leaking, the client would like us to verify the original engineering design to make sure that the proper PSV was installed for the application. To do this, they'd like us to confirm that the PSV has the proper orifice designation and relieving capacity at set pressure.

I hope that makes a little more sense!

 

[LittleInch]

Makes a bit more sense, but still don't understand why the orifice size and capacity is relevant to whether it's leaking or not. PSV's by their very nature are not supposed to be open during normal operation,only during over pressure events which have not been caught by the instrumented safety / shutdown system.

I would suggest that if you find one that is leaking, then note it's supposed set pressure on the name plate, the operating pressure of the line at the time and the design pressure of the relevant line. Then you can see if the operating pressure is too close to the set pressure (normally ~10% below set pressure, but can be less if you have a pilot operated valve) or whether the valve is passing when it shouldn't, hence needs to be maintained and set pressure checked.

To work out what the capacity should be needs a comprehensive review of the process safety calcs, which is not a straightforward task, but unless you've made some serios modifications to the plant since the design, shouldn't be an issue. Still nothing to do with leaking valves though.

I would double check what the client actually wants from this survey in this respect because it sure doesn't make sense to me.

My motto: Learn something new every day

Also: There's usually a good reason why everyone does it that way

 

[cheute79]

Does the client have the records that document the relief scenario on which the current PSV was selected? The sizing should be based upon a specific scenario, that documents conditions. Asking to verify sizing is just spending time and money. One can readily find a scenario, which might not be reasonable or defendable, that show that any PSV is under or over-sized. If the PSV is chattering, then it makes sense to check the sizing and scenario, because it is oversized or perhaps in disrepair.