1.ASME section 8 allows 21% overpressure for fire case? At the same time other relief scenarios (eg.blocked outlet) its 10%. What's the reason for allowing higher overpressure for fire case??
2. Consider i have a vessel, which is having a RV set pressure of 10 barg. RV on this vessel is sized both fire case and blocked outlet case. The governing case for the RV is fire case. During a overpressure scenario what will be the max. pressure the vessel can see. 12.1 barg (21%)or 11 barg(10%)??
Full Version: Why Asme Allows 21% Overpressure
umeshr,
I don't know the thinking that went into selecting the 21% overpressure allowance for fire but reducing that to 10% in most other situations. I do know that for well over 50% of all RV's I have seen, the fire case governed the sizing. While this doesn't necessarily mean anything, it does say to me that there would be a significant price to pay if the allowable fire overpressure was (only) 10%.
In answer to your second question, the maximum pressure that the vessel might experience, which indeed occurs during a fire scenario, is 121% * 10barg = 12.1barg. During any relieving event OTHER THAN FIRE, the maximum allowable vessel pressure is 11barg.
Doug
I don't know the thinking that went into selecting the 21% overpressure allowance for fire but reducing that to 10% in most other situations. I do know that for well over 50% of all RV's I have seen, the fire case governed the sizing. While this doesn't necessarily mean anything, it does say to me that there would be a significant price to pay if the allowable fire overpressure was (only) 10%.
In answer to your second question, the maximum pressure that the vessel might experience, which indeed occurs during a fire scenario, is 121% * 10barg = 12.1barg. During any relieving event OTHER THAN FIRE, the maximum allowable vessel pressure is 11barg.
Doug
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