1 reply to this topic

[_anggiaa_]

Hello.

 

i need to know about PSV fire case. i have gas scrubber with design pressure 1440 psig, rating pipe 600#, operating pressure 270 psig and set pressure psv at scrubber 570 psig, after calculated relieving temperature , i got  1014 (degree) F, is it safe for rating fllange pipe #600?? i just think relieving temperature not exceed from 1100 F (Carboon Steel). maybe iam wrong, gimme some advice.

 

thank you...

[paulhorth]

Hello,

What you need to consider is whether the vessel will rupture before the relief valve opens. If the calculated temperature of the contents is correct at 1014 F, then the vessel wall, at a temperature  hotter than that, will have a much lower strength than design, so it could fail at a pressure lower than the set pressure. Then you will have a BLEVE (Boiling Liquid Expanding Vapour Explosion) which is extremely dangerous.

I do not understand why the design pressure is so much higher than the relief valve set pressure, however this would have the effect of providing more thickness in the vessel wall, which would help.

In this situation, where there is a large difference between the operating pressure and the relief set pressure, the relief valve will not provide effective protection in a fire, and the vessel should be protected by water deluge and depressurusing (blowdown).

 

Paul