Pressure relief valve requirement

[Abitaieb]

Hello
Any one can Help by Answering the following Questions
If you have a vessel Which Have A design pressure Much Higher than Maximum operating pressure ( Cyclone designed for 10000PSI, maximum and the operating pressure only 2000PSI ) so there is no problem for closed outlet scenario but does the cyclone still require a Pressure relief valve , for fire Case ? If Yes , How to define the Set pressure for the fire Case ? Please advise any references (ASME , API , Engineering Book etc... ) which may answer and cover these questions .
Thankyou

[Hafiz Zakaria]

What kind of cyclone are we talking about? does it's outlet close during fire event? Set pressure should be set at MAWP or below MAWP, that's the basic rule . For vessel with fire case only, usually the max operating pressure is 90% of relief valve set pressure. This is what i've been practicing anyway.

Just remember the lower the set pressure means you're going to have a bigger relief load and of course, bigger PSV size. If you're confident with your vessel integrity, you can set it at higher pressure.

For blocked outlet you should look at the upstream pressure, is it possible for the upstream pressure to rise up to 105% of your vessel MAWP? If yes you should also take blocked outlet into your consideration.

For your reference you can refer API 520, 521, 526 and ASME sect 8.