4 replies to this topic

[Kwaku]

We are in the process of designing a new flare system and need guidance on acceptable operating pressure to be used as design basis, this would be the constant superimposed backpressure (on a normal day) behind any PSVs that tie into the flare header. From reading a related discussion on this forum, I noticed a reference to API-521 which specifies a minimum design pressure (or MAWP) of 50psig for the flare header system (including the flare knockout pot). The operating pressure would really be dependent on the amount of flaring in the process, but is there any recommended operating pressure range so we can make adjusments to the pipe sizing in order to stay within this range? Thanks!

[Bobby Strain]

The sizing and pressure are determined by the maximum relief load. That is where you start.

 

Bobby

[Kwaku]

Thanks for your response Bobby. Just to check if I understand your guidance correctly: So assuming the maximum relief load is pool fire scenario (global), I'd calculate the built up pressure for this load, and check how much margin I have between this value and the system MAWP, this will tell how much room I have for the normal operating pressure?

[Bobby Strain]

Almost. Then ascertain that the selected size is OK for some low set pressure valves.

 

Bobby

[Kwaku]

Thanks Bobby, this helps a lot.