Thanks both Latexman and lizking:
It is an existing one and BB (Sorry for that, Latexman, we use CONV, BB(Balanced Bellows) and Pilot for simplicity) is used for relief. I am following a rule without choked flow in tailpipe and 6" should be fine(back from 10 psig to discharge line of PSV)...
Thanks Latexman:
The key is that discharge pipeline reaches choked flow when back from 10psig to PSV discharge point. This is the reason why I can not figure it out. Thanks again for your input.
A scenario for fire case.
Pset = 525 psig
Relief Pressure = 1.21*525+14.7 = 649.95 psia
Relief Temp = BP@Relief Pressure = 220 F
Latent Heat: 95 BTU/LB
BB PSV is selected.
Max rated capacity is 64000LB/HR
Calculated area from Safety Engineer is API 2H3 (0.785in^2). Now the existing discharge...
