2 PSV's - 2 Vessels but 1 flame arrestor

[advsign]

I have 2 vessels that I want to tie together to go into a flame arrestor. During operation one vessel is at high pressure and the other one is at a low pressure.

Say if the current PSV outlet is 4", can I run 4" pipe to tie them both into a 4" flame arrestor or do I need to upsize the line.
If so which line would need to be upsized? The common line before the flame aresstor?

Thanks,

 

[MortenA]

Why would you want to route your discharge from a PSV through a flame arrestor?

Best regards

Morten

 

[meanderson3d]

It is never recommended to install a flame arrester in a PSV discharge line. At best, they impose a restriction. At worst, they can get plugged.

Relief valve discharge piping should be sized to limit built-up back pressure at the relieving valve and super-imposed back pressure at all other valves in the system. The limits on back pressure are a function of the set pressure of the valve and the type of valve (spring operated, balanced bellows, pilot).

Because of the limit on super-imposed back pressure, usually high and low pressure relief systems are kept separate. If they are tied together at all, it is usually immediately upstream of the vent (or vent scrubber, if you have one).

A good source of information is API RP 520 & 521.

Andy
New Orleans, LA
Petronyx Consulting Engineers, LLC

http://www.petronyx.com

 

[advsign]

The flame arrestor is desired because the vent gas will be Hydrogen.

Ken

 

[MortenA]

wouldnt it then be better to purge continuously with an inflammable gas such as N2?

Best regards
Morten

 

[skearse]

+1 on no flame arrestor.

N2, quenching steam, etc. are a much better way to go. Torisoidal ring (sp.) on the outlet to remove sharp-edged exit.