How to consider torsional moment in a body flange

[Mandeep1]

I am evaluating a body flange on a vertical vessel with an agitator on the top.

The agitator is located in the center of top head, head is connected to the body flanges.

Client has given considerable loads originating from the agitator.

Among other loads, the torsional moment is considerable.

I am looking for ideas on how to tackle the static loading and fatigue life from the torsional moment on the body flange.

What other techniques have been used to design agitator vessels.

Thanks.

best regards,
Mandeep Singh

 

[kywlium]

Hello Mandeep,


Usually the stresses due to torsional moments are low compared to the stresses due to bending moments.
Using PD5500-G or WRC-107 you see the same when only a torsional moment or only a bending moment is entered. Stresses due to torsion are low and often not mentioned in nozzle load lists from customers . Often only axial forces and bending moments are shown for this reason.

The shear stress which will develop in the circumference
of the vessel (or body flange)will not exceed 10 N/mm2 in most of cases.

With other words, when stresses due to torsional moment is that low, fatique due to these loads will never be decisive, so why bother to investigate.
A horizontal force at impeller level creates an bending moment which is actually rotating. This load is, in my view, the one which can cause undamped vibration , and therefore much more dangerous.

When you only take torsion into account, please calculate the shear stress, and you will see it is negligible.

Best regards,

Dick