5 replies to this topic

[Devandra Godara]

Hello everyone,

 

I am calculating relief load for one of the unit in refinery. Here We have a system where a control valve is connected to ESD. The ESD gets triggered during the failure scenario, which closes down the control valve. Now for calculating unmitigated load, the control valve was assumed to be in manual and ESD considered to fail (Hence open valve), But to calculate mitigated load (ESD to work), If considered valve to be in manual. Will the ESD able to close down a control valve taken in Manual.

 

Thanks 

Devandra Godara

[Chemitofreak]

As per my understanding the control elements linked with ESD should not be put on manual unless really-really and to be done under operator observation i.e. start-up/shutdown. If in manual, it will not close even if the ESD is supposed to close it.

[latexman]

DCS logic will NOT close a normally installed CV in manual.

[Pilesar]

ESD can be configured to close a CV in manual if it is completely independent of DCS. An example is the ESD control has its own solenoid on the valve air supply to reliably dump the air to the valve and close the valve when ESD is triggered. With no air to the valve, the DCS control mode would not matter. Instrument connection details should be configured by expert.

[Bobby Strain]

If it is critical, there should be a separate valve. If not, and it should be closed from ESD, there must be no handwheel on the valve.

 

Bobby

[Bitan729]

If it is fail to close valve then a solenoid can be installed in instrument air line going to the valve actuator. If ESD is pressed then the solenoid will get de-energized and closed the valve, regardless the valve is kept in auto or manual.