Allowable Stress during PWHT (after repair)
Allowable Stress during PWHT (after repair)
(OP)
I am calculating the crane force needed to permit safe 360° PWHT of a medium height, thin-walled vertical steel vessel. I can do the calcs (wind, dead weight), but I am having trouble finding an allowable stress for A285-C material at 1100°F, since that is beyond its permitted max. temp in section II-D.
And are there any other loads I need to consider?
And are there any other loads I need to consider?





RE: Allowable Stress during PWHT (after repair)
The concern is permanent buckling while at PWHT temperature for a vertical vessel. I would suggest using a percentage of the YS at temperature as a means to evaluate buckling forces. For similar material, the data I have seen at 1100 deg F indicates a knock down factor of 0.4 of RT yield strength.
RE: Allowable Stress during PWHT (after repair)
I'm not sure how to interpret 'knock down factor'. Does this mean I use an allowable of 0.4 x RT YS? Sounds a bit high, but I will consult my EPRI handbook for carbon steels ...
There is no doubt the vessel will be crane-supported, perhaps by two. Is wind still a consideration once you have decided on crane support? I have not yet compared the significance of wind-induced stresses to that of vessel dead weight.
Thanks for helping at this late hour.
RE: Allowable Stress during PWHT (after repair)
RE: Allowable Stress during PWHT (after repair)
Do you have that 1974 paper by Griffin?
My research has led me to API 579, Annex F. If I understand it correctly, allowables are calculated for external pressure in the creep range, and extrapolated into the PWHT range for that short-term situation.
RE: Allowable Stress during PWHT (after repair)
You're definitely on the right track.
RE: Allowable Stress during PWHT (after repair)
I am also attending B&PV Code week in Boston. Perhaps I will see you at the hotel bar......
RE: Allowable Stress during PWHT (after repair)
You might find this paper interesting;
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RE: Allowable Stress during PWHT (after repair)
I'm still trying to come to grips with the concept of creep buckling; wouldn't that depend very much on the geometry as well as temperature and stress? For example, I expect a longer heated band would increase vulnerability to compressive buckling of the shell.
p.s., while in Boston please don't add any more non-essential variables to Section IX ;)
RE: Allowable Stress during PWHT (after repair)