Safety Valve vent stack sizing

chogben · Feb 28, 2003

Greetings,

Does anybody have recommendations on techniques for sizing vent stacks on PSV discharge stacks; open or closed. I am familiar with the techniques of Benjamin, Liao, B31.1, and Miller of the BHRA.

Has anybody experience blowback on vents sized with any of the above techniques?

Chris

davefitz · Feb 28, 2003

The B31.1 and section VIII methods are based on Bechtel's Liao. To extend the B31.1 curves to longer stacks with more losses, you need to use the compressible flow equations in the original Laio paper. The Benjamin method is not conservative and cannot be relied on to prevent blowback, but it gives a cheaper /smaller stack size.

SooCS · Feb 28, 2003

API RP 521 is the best guide for you. Have you check it out?

chogben · Mar 6, 2003

SooCS
I have not read API RP 521. My employer doesn't deal with API specifications often so they are not kept up to date.

davefitz
Do you know why the B31.1 App II did not include the min. back pressure correlation that Liao has? Perhaps it was covered in the B31.1 equation for the chocking pressure?

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Safety Valve vent stack sizing

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