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PSV set pressure vs vessel design pressure

PSV set pressure vs vessel design pressure

PSV set pressure vs vessel design pressure

(OP)
Dear all,

One question occuring recently is when the design pressure of vessel is 5.5 MPaG, is it reasonable to determine its PSV set pressure as 4.5 MPaG with the operating pressure of 4MPaG?

Any comments about this item are greatly appreciated. Thank you.

RE: PSV set pressure vs vessel design pressure

Nothing wrong with setting the PSV lower than the mechanical design pressure of the vessel, but there must be a reason. Can you explain?

If the MAX operating pressure is 4MPag, with a PSV set at 4.5MPag, ratio would be 89%, which is just within the max permissible of 90% for a conventional PSV. You havent said if the MAX operating pressure is indeed 4MPag. This should cover all operating modes for this vessel, and should include reasonable process control margins for pressure excursions beyond the normal range due to process upsets.

RE: PSV set pressure vs vessel design pressure

Additional margins are also required for the PSHH setting, and there should also be adequate process safety time for the related ESDV to isolate the source of overpressure before reaching PSV set pressure.

RE: PSV set pressure vs vessel design pressure

On the other hand, it is okay to have PSV set at 5.5 MPaG as permitted by the Code. So, you can run the process to at the pressure up to the maximum limit of the vessel without a change needed for the PSV setting.

RE: PSV set pressure vs vessel design pressure

(OP)
thanks a lot for all the answers.

But if the operating pressure is 3.5 MPaG is it also OK for such PSV setting?

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