ASME VIII, extrados thickness

[PaulLag]

Hi there, hope you are fine !
Please, I am here to ask you an hint.
I am calculating an heat exchanger according to ASME VIII div.1.
I have following doubt:
In an hairpin the minimum thickness is in extrados after binding.

My question is : are there any formulas to calculate the thickness reduction with respect of straight tube ?

This is how I would operate
According to
ASME B31.5 504.2.1(b, c), with following requirement
Dmax - Dmin <= 0.08Dnom

I can utilize
ASME B31.5 504.2.1(a)

And then, considering
ASME VIII sec 1 UG-27(c), I consider the max between thicknesses got from eq 1 (for circumferential stress) and eq 2 (longitudinal stress)

PLease can anybody confirm me this method is correct ?
Are there different ways to calculate this ?

Many thanks

 

[Afox88]

I tend to use the formula in TEMA in the U-bend section. Forgive me I do not have my TEMA book in front of me so I can't tell you the formula without being sure I remembered it correctly.