Tube Rupture - Which upstream pressure to use for calculating flow?

[wolf359]

I have an exchanger where HP gas is cooled against LP cooling water. The LP side (and local pipework up until the block valves) has had its design pressure increased according to the 10/13 rule, therefore there is no need for a local relief valve in the event of a tube rupture.

However, in such an event it will still be necessary to relieve the HP gas via the cooling water network, and therefore the relief valve on the cooling water expansion vessel must be sized for this service, and a check must be made to verify that the return header piping is sufficiently rated for the back pressure.

My question is, what do I use as the pressure upstream of the rupture, in order to calculate the flow? Max operating? Design Pressure? Design Pressure + Accumulation? My own gut feel is to go conservative but I am under pressure to relax my assumptions.

Can anybody point me in the direction of any standards which I can use to justify a relaxation of my assumptions? I specifically need references; just stating that some allegedly experienced engineer on an internet forum told me to use my own judgement will not wash with this client..

 

[chemebabak]

1. Use design pressure
2. Review API 520 and 521 for reference. Of course, I could hold your hand and review it for you, but I would not want you to rely on an "allegedly experienced engineer on an internet forum" to spoon feed you the answer.

Good luck. Based on the language in your post you will need it!

 

[chemebabak]

Try posting this on Safety Relief Valve engineering (PSV) forum for more opinions from "allegedly experienced" engineers.

 

[wolf359]

Thanks. I already checked both API references but they do not state which pressure to use.