Pipe thickness requirements for high external pressure
Pipe thickness requirements for high external pressure
(OP)
I have a nozzle inside of a vessel that is no longer used and needs to be removed or isolated to remove the pocket it creates that can fill with hydrogen. The setup is a 8" Class 1500 nozzle on the outside of the vessel with a Sch. 80 8" nozzle on the inside of the vessel approximately 5" long with a class 150 flange. I would like to cut out the internal flange and weld a cap in its place. The issue I have is that the pipe/nozzle internally needs to be rated for an external pressure of 1749psig at 650F. The material is C.276 SB575. Sa is 24.6 ksi at elevated temperature. How thick would the pick need to be for the external pressure differential being 1749psig? I have stepped through UG-28 calculation and come up around 1". Hoping someone might be able to verify. OD of the pipe is 8.625. The inside of the pipe will be open to atmosphere.





RE: Pipe thickness requirements for high external pressure
I am doubtful that it matters if an unused nozzle fills with hydrogen gas inside of a reactor from a process or safety standpoint. However if it is bothering you why don't you leave the nozzle there and fill the space inside the nozzle with a short pipe stub or machined solid material. Then the volume of the dead leg will be drastically reduced without modifying the vessel, just the blind flange on the unused nozzle. I am curios as to why you want to do this???
Regards
StoneCold
RE: Pipe thickness requirements for high external pressure
RE: Pipe thickness requirements for high external pressure
Can you confirm? Also confirm 5" length, 8 5/8" OD.
Regards,
Mike
RE: Pipe thickness requirements for high external pressure
RE: Pipe thickness requirements for high external pressure
Given that you have a sch 80 pipe (1/2" thk), you would also have to remove the internal projection. In this case you might as well just weld a S.E. head directly on the inside surface of the shell, doing away with the pipe completely.
What about going in the other direction? As I understand, the safety concern revolves around someone unbolting the blind. What if you were to go the other way and put a pipe cap on the external pipe? The hydrogen would still be there, but you are removing the ignition source...
RE: Pipe thickness requirements for high external pressure
CS w/ 304 liner and Ni-Mo-Cr plate nozzle?
Not sure what to suggest, other than flush patch.
Regards,
Mike
RE: Pipe thickness requirements for high external pressure
RE: Pipe thickness requirements for high external pressure