Peers,

I am not a Pressure Vessel designer. We've engaged a designer to check design calculation of 5 scrubber vessels which needs to be re-rated from DP 2056psig to 2082psig for the purpose of production optimisation. All 5 vessels are identical design apart from following difference. 5th vessel has all the same design conditions apart from 3 nozzles of 4" dia (connected to shell) have different material schedule (and hence different nozzle pipe wall thickness) compared to other 4 vessels. All the other design conditions are identical. Now, the design calculations carried out on 5th vessel results that design pressure limit 2074psig. All other 4 vessels have met 2082psig.

I am not sure how such a minor difference in nozzle pipe sched can cause this difference in DP. Could repad thickness be a factor? What could be a possible solution to get all the 5 vessels for same rating in this case?

Thanks in advance for your comments/suggestions.