Bending stress in horizontal pressure vessel saddle base plate

[dannyo]

I am looking for a correct formula for the bending stress in the saddle base plate of a horizontal pressure vessel. The current formula I have has incorrect units.

fb = [(6*M)/(tb^2)] is the formula I'm using (units of lb/in instead is lb/in^2), where fb = bending stress, M = bending moment, tb = base plate thickness.

I have limited access to references so I would appreciate any formula or online reference site anyone could provide.

Also, if this is the correct formula could someone explain to me why the units are not in psi.

 

[TJW]

Have you found your answer to this? I just came across your post.
I think you're on the right track and the formula that you are using is for a unit length of base plate. The formula for the section modulus is S = b*t^2 / 6, and the bending stress is M/S Substituting you get M/S = 6*M / b*(t^2)
Then if you are looking at a unit length of the base plate, b=1, you reduce to your formula 6*M/t^2 (which actually is units of psi if you leave the b=1" term in the denominator.

 

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[jrmack]

I am surprised that so far temperature is not mentioned in your formulas (most of my pressure vessels involve temperature). If your pressure vessel has hot temperatures, you have a longitudinal growth that must be taken out by some longitudinal expansion (rather obvious and most likely taken care of) but there is a circumferential growth (of the shell) that causes a hogging of the saddle (the base plate will be of a lower temperature, therefore less thermal expansion, causing a hogging and bearing on the extremities of the saddle).

This may not be your case, but recently I was involved in a repair to the foundations of a rather large (thermal) vessel that was destroying its foundation.