Question for all the B31.3 guru's out there.
I have a packaged unit I am working on that has PSV's fitted specifically for relieving pressure during a fire [set at 47barg at 267C]. Normal operating conditions are 30barg and 80C.
B31.3 says very little about design to survive a fire, but on the basis that it is at least as likely to occur as an earthquake or extreme wind condition I am looking at checking the system over at 47barg & 267C and comparing the results against the B31.3 OCC stress limit @267C, as ideally we want the system to remain intact [if a bit charred] after a fire and not propagate the incident by further failures.
Since there is also significant thermal growth expected here - but probably only for one cycle, do I need to check the displacement stress range? I have a feeling that the system will be overstressed when comared to the allowable displacment stresses, but want to do the 'right thing'.
Also if we assume that we can increase the nozzle allowables on equipment by 1.33 we will proibably overload them as well during a fire.
Am I being overly conservative here? To me if we have a specified fire over-pressure protection, other safeguarding precations must also be applied.


Any comments, guidance or thoughts anybody?