Pressure safety (relief) valve design (B.D. Case)

[kkav]

Hi every Body,
For design of a PSV, four cases are always considered:
1)Fire, 2)Power Failure (P.F.), 3)Cooling Water Failure (C.W.F.) and 4)Blow Down (B.D.).I'm realised on the cases of Fire, P.F. and C.W.F. But I don't know what B.D. does mean in P.S.V. design? Would you please explain?

 

[Chance17]

My answer would be failure any and all inlet control valves.
This could be either gas accumulation or liquid overfilling.
In both cases you assume the normal vessel outlet is blocked and the pressure source control valve is 100% open.
People may argue this is a double contingency.
But consider someone trying to startup the equipment and the operator forgot to open the manual outlet valves.

 

[dcasto]

Blocked Flow is a typical as is failure of a control valve that could over pressure. This is typically a level control valve that normally dumps liquids but could dump gas.

 

[MikeClay]

I would assume B.D. would stand for blocked discharge.

 

[sheiko]

Kkav,
We are not going to guess when all you have to do is tell us what is the source/reference where you have found this "blowdown" term...Check the definition into it.

"We don't believe things because they are true, things are true because we believe them."