Hi Engineers, I want to ask. Are PRV + vents and drains actually needed in the Custody meter stream? Or does it serve its purpose only during maintenance?
@LittleInch thank you for your response. When I'm looking at custody meter P&ID/GA drawing, either for gas or HC liquid, some stream configuration has vent or drain after strainer or gas filter but some other dont have it installed to the metering stream even after the branch to the proover. That's makes me wonder, is it mandatory or depends on something to add vent/drain in metering system? or it's just me who overthink it? Because unnecessary branch just adds more uncertainity to meter calculation.
Depends on each system and where the isolation valves are etc.
The metering element is normally only part of the whole thing and you don't touch that bit, i.e. the 10D up and downstream or whatever.
Every thing else is dependant on the particular fluid, temperatures, configuration and to a certain extent the designer.
Some stick vents and drains EVERYWHERE, others only where you really need them.
Gas lines in particular can get away with no PRV, but liquid lines often have a TRV to avoid solar gain pressure rise.
There again some places have TRVs all over the place, some limit them depending on volume (never understood that tbh), should be any locked in section IMHO.
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I see, thank you again for your answer. Now I have better idea wether to add them or not. I would let people knows that I'm still open for their answer and experience. More story means better insight.
When you clean a basket strainer, you can trap air in it when it is being closed. If the strainer is large, it could be better to vent and purge the air out of it rather than allowing that air to carry into the meter and the downstream piping. It could also be helpful to have a drain in case a liquid meter requires maintenance, or if a gas stream is not entirely dry.
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