Oil Gas Separator PCV - Fail Open or Closed?

[GasOilEng]

Hi
I'd like to know which kind of PCV valve to flare should we install to oil gas separator, ie, Fail to Open or Fail to close.

Thanks in davance

 

[georgeverghese]

Presuming there is no process safety function (i.e it is purely for process controls and it is not meant for ESD depressuring either), I'd go for FC since the hazard imposed by a PCV to flare failing full open are much worse than if the valve were to go FC (flow over load to flare system; high liquid entrainment in vapor stream to flare).
Besides, you've probably got other safety trip loops to address high pressure events on this separator, and you'd most likely want this PCV to go to close position during an ESD, given that one of the causes for an ESD could also be low pressure on the plant main instrument air header ??

 

[LittleInch]

I agree, but without knowing what else is there it's difficult to say.

A PCV should not be a pressure safety device and therefore should fail close. There should be further higher integrity devices ( Spring relief valves, bursting discs etc) which protect against high pressure.

I'm more interested to know what this PCV is used for - normal operation?? to flare?? That's a criminal waste of gas if it is.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[MortenA]

If its a kind of spill over valve then i would say fail close. If it opens then it would "drain" the pressure of of your upstream vessel. Fail close it will perhaps have to impact or sooner or later the system will trip.

Best regards, Morten