PSV for piping protection

[gColbert]

I need to protect a 1 1/2" pipe from overpressure, it is on the outlet of a desuperheater. The conditions are:
11321 lb/hr steam
665 psia
740 F
Set pressure of PSV is 730 psig.
I need to know where to start.
Can I take the conditions of saturated steam at 730 psig, subtract the above conditons and size the psv for that flowrate? or is it more complicated? Assuming, although incorrectly, that the above conditions are for saturated steam.

 

[dcasto]

go to Mercer relief Valves and they can walk you through it.

Typically, you do not see a lot od lines being protected as they are useually protected by some vesssels relief valve. The only time you need to protect a line is when there is a pressure letdown and you have a specification change in the piping and need to protect in case of a control valve failure OR if you expect a fire or thermal case on a line that can be isolated.

 

[gColbert]

Thanks dcasto. Originally, I was confused on where to start, since all I have done is calc's on vessels, and the fire scenario was the worst case for each of those. It is hard to imagine a fire affecting a 1 1/2" pipe though. I am actually finishing up an incomplete package for another engineer, who was offsite. He has since returned and gave me the rest of the package and we walked through the valid scenarios. It is coming into focus now, just a bit overwhelming with all of the incomplete info.