Hello everybody,

I have heater which is direct fired tube oil heater; the PSV is installed at the piping discharge line and we want to size it for thermal relief case for example as you know if we have blocked flow around the heater and we still heating the oil, I check API 521 and understand the procedure and calculate give me small relief load but thought there will be another way to calculate by calculating the difference in specific volume at differnt temerature, what you think.

My system is for crude oil pumping plant and we need to heat the oil so it will not wax during the operation,the design pressure for the heater is 63barg

Do you have any relevant information about this so I can proceed and evaluate this PSV?

your comments is very much appreciated.

Thank you,

There is no way to say this without sounding like I am being "nitpicky" or too detailed, but . . . . this is NOT the traditional "thermal relief" case. The traditional "thermal relief" case has heat added to the system through ambient heating only. No additional heat is added to or through a heat exchanger; it all comes from the surroundings.

mabu - in your scenario you have a blocked outlet scenario. It is not a traditional "thermal relief" scenario. And, yes, you are on the right track.

Thank you Latexman

Is it the same answer if we consider thermal expansion? or will be differnet consideration.

We start to think of calculatiog the fire case relieve load and check which one will be higher to design for, what i have to take into my consideration for this case, when i used HYSYS just to check my relieving temperature (Disgn temperature ??) and relieving pressure (Design Pressure ?? ) it didnt give me vapour or i can design for liquid (dont think) as we heating more will get vapour ,not sure which conditions to use.
what about the area is it better to use the tubes area or the fired box area.

please advice.

Regards