Stress in shell due to thermal expansion of a heat exchanger

[kyong]

I am very wondering why heat exchanger design methods don't consider shell thickness in view of longitudinal stress(compression or tension) due to thermal differential expansion of fixed tubesheet type heat exchangers.

I looked into K.A.G. Miller's method to design fixed tubesheet and ASME Section VIII-Div 1 App.AA.

Miller's method uses thickness of shell and properties of shell material to calculate longtudinal stress of tubes and stress in tubesheet. But it doesn't mention about shell stress.

On the other hand, ASME method does calculate shell stress , i.e., membrane stress due to interaction with tubesheet and bending stress due to the same one. It donesn't provide longtudinal stress of shell. Is this, by any chance, because longtudinal stress is not important or not necessary to calculate?

Does any one have any idea about this issue?

kyong

 

[prex]

This point is addressed in TEMA standard, where the longitudinal shell stress is calculated and compared to the code allowable stress.
App.AA addresses specifically the tubesheets, so in my opinion you would not be relieved by it from checking shell stresses.
Of course it would be a quite odd condition that the shell longitudinal stress is the limiting factor in a heat exchanger calculation, but you are right in raising the question, it is not an impossible condition. prex

http://www.xcalcs.com

Online tools for structural design

 

[Shmulik]

TEMA Standard: RCB-7.22 Shell Longitudinal Stress.

 

[kyong]

prex, Shumlik,

Thank you very much.

I'll calculate the shell longitudinal stress with TEMA formulas. Should I find anything interesting, I'll tell you guys.

 

[kyong]

prex, Shumlik,

I calculated the shell longitudinal stress with TEMA formulas. I'm not 100% sure if my calculation is free of mistake because the formulas are pretty complicated. But I hope the calculation is correct. The result was around 9000 psi compression at worst condition, so I have some margin for weight load and other misc loads. Now I became not worried. Thank you guys again.