Outlet line size of PRV 3

[KVVS]

Dear Sir,
During review the P&ID, I saw PRV out let line size is less than inlet line size. is it possible ?
PRV having 4.5 barg set pressure & connected with LP flare header.
I understand inlet line size & outlet line size govern by different factors like but usually outlet line size is greater than inlet line size.
Please guide me at that matter . thanks in advance

 

[Latexman]

It is probably a mistake. Investigate it.

Good luck,
Latexman

 

[don1980]

KVVS - what's relevant is the inlet and outlet size of the PSV and not the piping. The ASME rule says the inlet pipe can't be smaller than the PSV inlet connection, and the outlet pipe can't be smaller than the outlet connection.

It's possible this installation is OK - but I can't say since you referenced the in/out pipe size rather than the in/out PSV size.

 

[TD2K]

As Latex said, I'd investigate it but it's possible the design is fine. The inlet line has likely been sized to keep inlet line losses to less than 3% of set so if you have a long inlet line or a viscous fluid that can increase the required diameter. For the outlet line with a bellows PSV, the backpressure can be up to the order of 50% or more depending on the derating factor so a smaller line is possible

 

[KVVS]

Thanks for reply

 

[poli60]

The principles reported by TD2K are almost "bible"... but, in 30 years' work and more than 1000 PSVs specified/verified, I've never seen the outlet line bigger than the inlet one. Look carefully at the calculations... and if you don't find the mistake I'd advise you to apply the following rule of thumb: increase (at least) one size the PSV outlet to obtain the diameter of the downstream piping.

 

[poli60]

Sorry... I wrote bigger instead of smaller.
Anyway, if you share some basic data a quick check could be made to give a more professional answer; as a minimum:
- set pressure and back pressure
- mass flowrate and density of fluid
- vapor fraction at in/out conditions
- in/out size of PSV and lines

 

[KVVS]

I am fully agreed with poli60. me too never see such thing in my past projects. I already put note regarding out let size.
thanks everyone .