Please give me the suggestion & comment.

I come across one case for 24” gas blow down. Due to the process design concept for blow down, velocity = 540 ft/sec, A = 24”, density = 0.9865 lb/ft3. So the momentum force at elbow is 11,980 Kg (F= density x V^2 x A) and the reaction force at the exhaust is 43,816 kg (from API 520). You can see that the force is very high. I analyze by input the reaction force(F1) at the tip of stack and input the momentum force(F1) at all elbow. The load cases similar as below

1) W+T1+P1 (OPE)
2) W+T1+P1+F1 (OPE)
3) W+P1 (SUS)
4) L1-L3 (EXP)
5) L2-L1 (OCC)
6) L3+L5 (OCC)

Is the acceptable method for static analysis?

I am waiting for your comment.
Best Regards,
Kach