UG-45(b)(2), ASME BPVC Sec VIII, Div 1

[samuelliu]

Does "...by using the external design pressure as an equivalent internal design pressure..." here means trE = (PE/P)*tr (as we always can calculate tr easily)? Where, trE - Required thickness based on external design pressure; PE - External design pressure; P - Internal design pressure; tr - Required thickness based on internal design pressure.

 

[esf]

I understand it to mean that you use the external pressure in the calculation for the shell or head thickness as if it were an internal pressure.

So if your external pressure is 15 psi, then you would use 15 psi in the shell (of head) thickness calculation in order to determine the minimun nozzle thickness.

 

[samuelliu]

Yes, "...in the formula for the shell or head..." there means to calculate it for the shell or head, however, my question is regarding the interpretation of "...by using the external design pressure as an equivalent internal design pressure...", and say more clearly:

trE = (PE/P)*tr

Where, trE - Required NOZZLE thickness based on external design pressure; PE - External design pressure; P - Internal design pressure; tr - Required SHELL/HEAD thickness based on internal design pressure.

 

[prex]

Don't understand your point: UG-45(b)(2) states 'for vessels under external pressure only...'. So, what's the value for P you are speaking about?
esf has the correct answer.

prex

http://www.xcalcs.com

Online tools for structural design