3 replies to this topic

[K J]

Dear sir,

       why pressure control valve(PIC) of reactors and vessels in hydrocarbon or any other system are are kept fail safe close condotion. some time it may happen that vessel is under pressurisation for leak test and if its pressure control valve(PIC) close in fail safe condition it will creat abnormal condition.

[fallah]

KJ,

 

Probably,a PSV is there to protect the reactor against overpressure due to closed position of PV failure. Such PVs are to be considered to keep required pressure constant and if would have fail open characteristic, will cause loss of inventory in failure open condition...

[Lai.CY]

Hello KJ,

 

A control failure (due to bad signals, cut off signal and so on) will normally cause the valve to go to it's fail position. The intention of a pressure control valve typically is to control the downstream (or upstream) pressure. Therefore, if it fails in the open position, the downstream system might experience an overpressure (especially if there is a high pressure and low pressure interface, i.e. difference in design pressure or a flange pound rating break).

 

Also, there is no reason due to control failure, the PCV (pressure control valves) goes to it's open position (if it is a fail open valve) and lose all it's containment to the flare (if it's connected to the flare).

 

In an event of emergency, a blowdown valve (BDV) will do the depressurizing instead of a PCV. Some design, in the event of an emergency shutdown (ESD) when a system is isolated by the Shut Down Valves (SDV), the PCV will have a lag time to allow the pressurized gas upstream of the control valves to depressurized when the BDV opens, before going to it's fail position.

 

Hope I am answering to your question.

Edited by Lai.CY, 16 April 2014 - 08:56 PM.

[K J]

thanks Fallah and Lai. CY  for this information.