PSV question

[garciaf]

Here is my issue.
I have 3 pipelines that comes from sea, these go throught inshore until the plant. In plant (the entrance) there is a relief valve for each one (Diesel 26 inches, Regular Gasoline 16 inches, Premium gasoline 12 inches). the relief valve of 26 inchees diameter Diesel is set to 186 psig, and the line is constantly releiving in the day (Hissing/due to the sun)the pressure measure in a manometer (180 psig)and the temperature is 38 celcius. the value measure of the pressure is less than the set( but I imagine that is for the counterpressure at the other side, this piping continue to the discharge line of a pump,(Downstream of the relief valve I am describing there is a check valve) but my question is why the others do not relief?
Please Help me to understand.

 

[mk3223]

Are the PSV set points of the other two pipes the same as the PR of the Diesel line?

IMO, it seems that the PSV may not be calibrated properly, so it relieves at lower pressure than the set point. Or, you may verify the accuracy of the local PI.

 

[LittleInch]

garciaref,

That is a strange system you've drawn.
First you show flow going to the sea not from the sea?

A relief valve around a check valve is not common and the issues of relieving to a closed in section are notorious.

A lot depends on the type of valve you have ( balanced bellows, pilot, standard??) and what the pressures are upstream and downstream of your check valve.

It is rare to find a check valve holding against pressure to the extent that it can cause a TRV to lift.

do you have a P&ID or are you sure this is where it is piped?

However diesel has quite a high expansion co efficient and constant hissing of hydrocarbon lines locked in in the sun is quite common.

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