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[Abdessamed1961]

Hello everyone

I need your help about line sizing for PSV's, i'm sizing PSV's for a pipeline transporting a gas with the following data:

MW=                        20.53 (mostly methane 71%)

Flowrate=                 320 000 kg/hr

Density upstream = 184 kg/m³

Temperature=          100 °C

Pressure=                240 bar

Z factor =                 0.89

Cp/Cv=                    1.55

i used HYSYS safety analysis for sizing, i choosed blocked outlet scenario as the worst case scenario, so i discharged all the flowrate, HYSYS suggested 3 pilot PSV's, the simulation selected 2 J 3 (2500 x 300)  for each PSV for a flowrate of 106 666 kg/hr, the problem i'm facing now is sizing the downstream lines, i took a mach number of 0.7, density of 2 kg/m3 at relieving.

hand calculation gave me a 10" pipe and the flare header around 20", these results seem  weird to me, i would like to know if these are reasonable or my calculation are missing something.

thank you.