PSV Assembly

[emptyxp01]

Is bleeder required between the isolation valve and PSV at the discharge side?
As per API, it shows a typical assembly of PSV with a bleeder at the discharge side, but here on my current project(existing plant) they don't installed bleeder at the discharge.

 

[Gator]

This can be complicated and I'm no safety valve expert.

I suppose it would largely depend on the fluid.

If you're shutting down just one unit in a facility and don't trust the seal on the PSV's downstream block valve, you might want to check it by carefully cracking open the bleed valve for backpressure after closing the downstream block valve.

Bigger brains than mine hang around here, so you'll likely get more thoughts. Good question.

Paul

Piping Design Central

 

[emptyxp01]

The fluid for the PSV assembly is a process commodity.
It was a closed type relieving system which was most probably the commodity inside is toxic.

My conviction is the reason for the bleeder on the discharge side is to release the build-up pressure between the psv and the isolation valve in case you shut off the valve and want to remove the psv. I'm just wandering about the setup in the existing plant which doesnt have a bleeder, on how they release the build up pressure. Do they crack the pressure on the flange connection?is that safe?

 

[LittleInch]

Emptyxp01, I your conviction is correct. In shutting off the discharge valve, hopefully after the inlet valve, you are creating a trapped volume of product. If it's a common flare / vent system these often run at a small Perdue which is then trapped between the isolation valve and the psv. If the volume is small then in reality you've probably not got an issue, but if large volume or toxic, then any removal of psv would result in a release.

If you've got a liquid, you could have issues with thermal expansion causing excess pressure.

Cracking flanges to vent / drain pipework is not safe, but has been used in many instances in the past to do just that.

Hence I think you do need a bleed valve between the two, but you do need to think about the volume and would be an issue when coming up with a method statement and risk assessment to remove the psv.

My motto: Learn something new every day

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

 

[Gator]

I like this new LittleInch guy, is he someone's long-lost brother, or what?

Piping Design Central

 

[LittleInch]

Ask BigInch....

Kind of a bit addictive at the moment., I'm sure it will pass....

My motto: Learn something new every day

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

 

[Latexman]

Sounds like this time the pipe fitters will have to put on the required PPE to break the flange after it has been properly prepared and locked out. Please get involved and make this safe. Treat it as if you were turning the wrenches. Then, install a bleeder on your project, so next time it is inherently safer.

Good luck,
Latexman

Need help writing a question or understanding a reply? forum1529

 

[emptyxp01]

thanks all for the reply. I will try to persuade my lead regarding this one.
Unfortunately, the current design instruction in our project is to make our design same
as the existing(like to like).Hopefully this will be changed.

 

[LittleInch]

At this point I always recommend the written approach setting out to your lead the API clause and spec, other advantages or requirements, safety issues and your clear recommendation to install these small additional items. It's not as if you're asking for anything major.

A good spot though.

My motto: Learn something new every day

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