Appendix 41 - external pressure
Appendix 41 - external pressure
(OP)
Hi,
I was wondering if anyone knew if ASME Section VIII Division 1 Appendix 41 can be used for external pressure calculations?
The definition of P in Appendix 41 is design pressure and does not refer to internal or external as it does in UG-34 (UG-34 is only for internal pressure, see interpretation VIII-1-89-206).
From my understanding Appendix 41 is really just UHX 12 U-tube tubesheet design procedure with Pt=0, and configuration d. The interesting thing is that UHX 12.3 defines Ps as the shell side design pressure, for vacuum service use a negative value for Ps.
Would that be the case with Appendix 41?
The confusion for me is in the external pressure restriction in UG-34 for blind flanges. I don't understand from the Roark equation derivation how external pressure would result in a different thickness than internal pressure. If you absolute the moments similarly to UHX the results are same.
I was wondering if anyone knew if ASME Section VIII Division 1 Appendix 41 can be used for external pressure calculations?
The definition of P in Appendix 41 is design pressure and does not refer to internal or external as it does in UG-34 (UG-34 is only for internal pressure, see interpretation VIII-1-89-206).
From my understanding Appendix 41 is really just UHX 12 U-tube tubesheet design procedure with Pt=0, and configuration d. The interesting thing is that UHX 12.3 defines Ps as the shell side design pressure, for vacuum service use a negative value for Ps.
Would that be the case with Appendix 41?
The confusion for me is in the external pressure restriction in UG-34 for blind flanges. I don't understand from the Roark equation derivation how external pressure would result in a different thickness than internal pressure. If you absolute the moments similarly to UHX the results are same.





RE: Appendix 41 - external pressure
I'm like you, I don't see how a flat plate cares which way the pressure acts.
Regards,
Mike
RE: Appendix 41 - external pressure
A little off track but for a external pressure thickness calculation for a blind flange, you could use UG-34(c)(2) eq. 2 modified by 2-11? I think the below would be correct, you only modify the gasket seating load by the W value in 2-11.
t= G x sqrt((0.3 x Pe)/(S x E) + (1.9 x (3.14 / 4 * G^2 * Pe + 2b x 3.14 x m x Pe) x hg) / (So x E x G^3)) (operating)
t = G x sqrt(1.9 x ((((3.14 x b x G x y)+Ab x Satm)/2) x hg) / (Satm x E x G)) (gasketing seating)
Pe= external pressure
G= diameter of gasket load reaction
S = allowable stress (at operating (So) & gasket seating (Satm))
E= joint efficiency
hg= gasket moment arm
b= effective gasket width
m= gasket factor
Ab= total bolt area
y = gasket unit seating load
RE: Appendix 41 - external pressure
t= G x sqrt((0.3 x Pe)/(S x E) + (1.9 x (Wm1e) x hg) / (So x E x G^3)) (operating)