Similarly while modeling flare systems in Aspen Flare system Analyzer, putting in the correct PSV outlet flange is required. I have noticed that it does change the back pressure on PSV. So yes, uptill the PSV outlet flange.
There was a similar discussion in our company. The situation was that there was a scenario where a single valve was relieving gas to an atmospheric vent. A couple guys argued that the pressure "available" at the tip of vent is basically pressure at the inlet of relieving valve (not PSV, consider...
I would agree with joerd. There is just the "3%" rule for the grass root design as per API guideline. Although I have seen engineers take slightly higher pressure drop acceptabe in older/existing facilities.
So when you design for 3% od set pressure of PSV as pressure drop (inlet line)the...
