5 replies to this topic

[srinivasan]

Hi everyone
please ref the attached sheet.

where vessel A has psv sized for fire.which is set at 100 psig and the Design pressure is 100 psig.and operating pressure is 60 psig @160 F.
My protected vessel is "B" which has MAWP of 84FV @500F.and Vessel B is not in the fire Zone.Can you please help to solve the problem.

My question is we have to consider the maximum 121% of relieving pressure from upstream vessel is going to feed my vessel for feed over pressurization scenario.please answer my query.

Regards
A.Srinivasan

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[djack77494]

Srinivasan,
I hope that I am not understanding your query correctly because you are presenting an unsafe situation. You say your vessel's MAWP is 80 or 84 psig but the PSV on this same vessel is set at 100 psig. This is an unsafe (and illegal, depending on jurisdiction) situation. The PSV setpoint must be no higher than the MAWP of the vessel. Beyond this comment which I view of much higher importance than your actual query, I am having trouble following you. Speak to each vessel independently. It sounds as if you are asking about sizing a downstream vessel's PSV based on it being overpressured from an upstream vessel's fire case. That does not make sense. Please reformulate your query more clearly, considering the above.

[srinivasan]

Srinivasan,
I hope that I am not understanding your query correctly because you are presenting an unsafe situation. You say your vessel's MAWP is 80 or 84 psig but the PSV on this same vessel is set at 100 psig. This is an unsafe (and illegal, depending on jurisdiction) situation. The PSV setpoint must be no higher than the MAWP of the vessel. Beyond this comment which I view of much higher importance than your actual query, I am having trouble following you. Speak to each vessel independently. It sounds as if you are asking about sizing a downstream vessel's PSV based on it being overpressured from an upstream vessel's fire case. That does not make sense. Please reformulate your query more clearly, considering the above.

i have given my input.

[JoeWong]

My question is we have to consider the maximum 121% of relieving pressure from upstream vessel is going to feed my vessel for feed over pressurization scenario.please answer my query.

What is your question ?

[skearse]

I think that what he is asking is whether or not he should consider any vapor generation from vessel "A" during an external fire in the fire zone around "A" as a cause for overpressure in vessel "B".

My thought would be that no, if vessel "A" has a properly sized PSV to handle the vapor generated during a fire around "A," you would not consider the excess generation from the 121% (121 psi in this case) when sizing a PSV for "B." HOWEVER, I would say that you DO need to consider the vapor generated in Vessel "A" that would cause vessel "B" to exceed its MAWP-i.e., the vapor flow from "A" that would be in excess of the vessel "B" MAWP (84 psi) but less than the pressure at which the vessel "A" PSV begins to lift (100 psi). It may make it easier if you want to consider setting the vessel "A" PSV for 84 psi...just food for thought. I would also note that this scenario would not be an external fire around vessel "B", and thus would be a 10% overpressure process related upset rather than a 21% overpressure external fire scenario.

[JoeWong]

I think that what he is asking is whether or not he should consider any vapor generation from vessel "A" during an external fire in the fire zone around "A" as a cause for overpressure in vessel "B".

Based on what you have interpreted...
generally there will be a SDV for proper segregation of fire zone between fire zone around "A" as a cause for overpressure in vessel "B". Only PSV within same fire zone will be considered relief simultaneously. Besides there is limitation in term of area i.e. 2500-5000 ft2.