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Allowable Stress during PWHT (after repair)

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?   

RE: Allowable Stress during PWHT (after repair)

brimstoner;
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)

(OP)
metengr,

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)

This is a short-term creep problem - specially creep-buckling.  There is published creep data at typical PWHT temperatures for most materials.  Develop a isochronous stress-strain curve (based on the duration of the PWHT), and then you can base an "allowable" on that.

RE: Allowable Stress during PWHT (after repair)

(OP)
TGS4,
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)

I may back in my office.  I am currently attending Boiler and Pressure vessel Code Week in Boston.  I can also ask fellow Code Committee members if they have that paper.

You're definitely on the right track.

RE: Allowable Stress during PWHT (after repair)

TGS4;
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)

(OP)
Thanks gents.  The paper describes my situation very well.  I am doing this without software.  

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)

AMEN to no more variables being added to ASME IX.

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