In PSV open discharge is it required
1) to impose reaction force(momentum component of reaction force cl 2.4.1 in API 520 part2 ) at every elbow of discharge
2) if imposed, can it be assumed to act simultaneously at all elbows(same occ case for all elbows)
3) And if discharge pipe has slug component then can both (slug+ mom reaction comp) be combined in as single case

dear frnd

1)Psv forces are to be fed in the Caesar model but there is a crieteria for this.
1. if open PSV.
2. if inlet line size greater than 8" in Closed PSV.

the above crieteria may change as per your company's requirement,but is refered usually.

2)forces not at all elbows only at first supports on either inlet/outlet side or both.

3)slug is a different issue.But yes the slug force and reaction should be added and incorporated in the model for accurate analysis.

The change in momentum load (quickly) travels from one elbow to the next with every subsequent elbow equalizing the imbalance on the previous elbow.
On an open discharge system you also have the jet load (exhaust pressure times exit area) at the exit. I would consider both the momentum load and jet load at the last elbow before discharge. If there are long runs, there may be enough time (the pressure wave is traveling at the speed of sound) for the temporary momentum imbalance to be significant between that individual elbow-elbow pair.