Dear professionals,
API 520 II says the nominal size of inlet piping to the relief valve must be the same as or larger than the nominal size of the relief valve inlet flange connection. This is a common practice in the design.
We are currently facing a case at which the pressure vessel service is to be changes to a new service. The new calculation of the relief load shows that the new relief valve is to be one bigger size than the original one (the original is 1.5" G 3" and the new one is 2" H 3"). The issue is that the nozzles on the vessel are 1.5" and it is extremely difficult to revamp these nozzles on the 50-year old vessel. The calculation shows that the piping expansion from 1.5" to 2" is not bad and acceptable hydraulically. So, is that enough to waive the above API 520 II requirement? Or is there something overlooked?
Appreciate your thoughts and your usual help....
Regards,
Edited by Vegeta, 10 May 2021 - 06:57 AM.