safety valve sizing

The temperature comes from the process and the event that is causing the overpressure. For example, if you are pumping the acid and are sizing the relief valve for the event of a valve being accidentally closed, the relief temperature is simply the normal pumping temperature.

For other relief cases, the analyses can be more difficult, what is the case(s) you are looking at?

TD2K, thanks for the reply, the application for these pressure relief valves is on railcar tanks, the formula establishes a flow which is sufficient to prevent catastrophic failure of the tank when a pool fire surrounds the tank. The tank exhaust to atmosphere through the PRV.
In the past,I have flow tested valves using air, pushing 20,000 scfm through the valve with the supply air temp at 520R and the temp at the nozzle being 475R. The flowing temperature is not the temperature of the product within the vessel.
Hope this help
Barry17

Barry17:
You should get a copy of NFPA 30 "Flammable and Combustible Liquids Code". There is a formulas and a procedure to calculate the heat input due to a fire under a tank and the Pressure Safety Valve flow rate to vent off the vapor to keep the pressure below the vessel design pressure.

You can convert the heat input to a flow rate and conver the vapor flow rate to a equivalent air flow rate in Standard Cubic Feet per Minute or Hour.

Having the air flow rate SCFM or SCFH will allow you to look up a valve in the manufacturers catalog that will suite the need.

I have a spread sheet based on NFPA 30 which will do this calculation. My Email address is dlandis@tpdesignbuild.com
Email me your Email address and I will send you a copy.