External Pressure on Vessel

[AlexRG]

Hi.. Im currently using pv elite as the software aproved by the client, but im getting an error, induced by external pressure. I would like to know if it is mandatory to run an external pressure design on the vessel, using 14.7 psi as the external pressure, the issue its that im obtaning a shell thickness too high. Its there any criteria to input the external pressure in the design process. Do I have to use 14.7 psi or just 0 psi.

Thanks

 

[stanweld]

You do not need to design for full vacuum unless the vessel will experience full vacuum in service.

 

[AlexRG]

Thank You!!!

 

[AlexRG]

One more thing, wich part of ASME code states that I should use full vacum design??. the vessel has an operation pressure range of -0.2/1.0 BAR(g). In this case should I use 14.7 psi of external pressure???

Thanks

 

[VeryPicky]

Vessels that are steamed out during shutdown may also require full vacuum design. Owner/User should specify those conditions.

Putting Human Factor Back in Engineering

 

[djack77494]

There are alternatives to just increasing the wall thickness to design for vacuum. For example, you could add external stiffening rings to strengthen a vessel to be able to withstand vacuum.

I've seen it commonly done to design for "Full Vacuum" = (14.7 psi)if a vacuum condition might exist. If you want to design for a lesser vacuum, you must determine the worst case vacuum that might be generated. If you can do that, then it would be alright to design for that less severe condition.

Doug

 

[jodyed]

I have had designs where I need externials and to compute I changed Head designs and/or configurations to maintain shell thickness. The expense for Heads was less than the shell segments.

Hope this might help in your future.

jodyed

 

[jodyed]

In reference to your using a software program to calculate your designs, I to us one because it is so much faster. In it, If I enter any externial value other than "0" my software automatically computes externials. The real relivence, in most cases, to externials seem to come when calculating Nozzels, i.e., manways, clean-outs, etc. Even with externial rings, the externials seem to always wind up calling out the need for Repads at the nozzels joint to the parent shell. Be sure to check this out.

Good luck

jodyed

 

[charpyboy50]

Per UG-116 Section VIII Div 1 is it now mandatory that all ASME nameplates address external working pressure even if its not within there design scope.