Allowable stress for nozzle load
Allowable stress for nozzle load
(OP)
When a nozzle load on a ASME Section VIII, Div.1 vessel is based on pure thermal stresses, what allowable stress value may be used ?
Our customer believes that for a pure thermal case, that the allowable material stress may be multiplied by 1.5X, but can not point to specific code section that says this.
Can someone please advise on any knowledge of this ?
Thanks
Bangrod
Our customer believes that for a pure thermal case, that the allowable material stress may be multiplied by 1.5X, but can not point to specific code section that says this.
Can someone please advise on any knowledge of this ?
Thanks
Bangrod





RE: Allowable stress for nozzle load
See VIII Div. 1 UG-23(e). For a better understanding, take a look at Div. 2 App 4, in particular Fig. 4-130.1. Going to 1.5*S would be considered by most to be conservative with a thermal loading: You could go as high as 3*S. However, going to 3*S requires a lot of confidence that you have evaluated everything. Try to keep local primary + secondary stresses below 2*S and you'll save yourself some trouble.
Seipp, George, and Morrison have presented two papers at the ASME PVP conferences which provide at least one example in which thermal loadings induced stresses which behaved as primary, not secondary stresses. If you're looking for the paper at the ASME web site, it's number PVP2005-71535. I'd ask your piping stress guy what the free thermal growtn of the piping would be if the vessel wasn't there. If its 3 feet, I'd be wary. If its 1/2 inch it'll behave as a secondary stress.
jt
RE: Allowable stress for nozzle load