Paralleling multiple safety relief devices for a pressure vessel

[plantprowler]

When (a) a relief valve is paralleled with a rupture disk / another relief valve is it acceptable to use the same pressure vessel vessel nozzle with a branch in the piping (with piping size suitably selected, of course) or is it necessary to use separate vessel nozzles to attach each relief device?

 

[Latexman]

I assume you mean 2 x 100% capacity redundancy. It depends on the risk analysis. If the risk is acceptable to you and your company for the common cause failure of the nozzle, then yes it is acceptable. If not, then it is not. For example, it may be acceptable in a clean, solvent-like chemical service, but it may not be acceptable in a pluggage-prone polymer service.

Good luck,
Latexman

To a ChE, the glass is always full - 1/2 air and 1/2 water.

 

[plantprowler]

Thanks @Latexman

Yes, I did mean 2x100% capacity redundancy.

But out of curiosity, would your recommendation be any different had the paralleling been for other reasons. e.g. Multiple relief scenarios, or split capacity etc.

 

[sshep]

Hello Plantprowler,

It is permissible to have a single nozzle serving two relief valves, or even have them on the process piping. Check API RP 520 part II- Installation of pressure relieving devices; which includes typical layouts. The key design parameter is the allowable pressure drop in the inlet piping. For a conventional relief valve, the inlet losses must be no more than 3% at full flow to avoid "chattering" of the relief valve.

best wishes,
SShep