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cyclic load on the agitator nozzle

cyclic load on the agitator nozzle

cyclic load on the agitator nozzle


Dear sirs,
I am doing pressure vessel design in that vessel one agitator nozzle is on the top head, in the data sheet
specifies Fatigue analysis to be done
I have no idea how to perform the fatigue analysis
i hope anyone will guide me to perform the calculation

thanking you
Babu Mathan
Pressure Vessel Engineer.

RE: cyclic load on the agitator nozzle

The magnitude of the fluctuating loads will need to be obtained from the agitator manufacturer. In my experience, they usually do not give the loads in the form of mean load and alternating load that would be required to do the fatigue analysis. The loads given are usually pseudostatic loads that have a dynamic load factor built in.

Once you have the loads, the stresses are calculated using WRC 107 methods, which you probably already know. To evaluate the fatigue, use either the Soderberg or Gerber criteria to evaluate the fatigue. If you are not familiar with these criteria, check just about any good machine design book.

Soderberg uses equation:
(Sm/Sy) + (Sa/Sn) = 1/N

Where Sm = mean stress
Sy = yield stress
Sa = alternating stress
Sn = endurance limit stress
N = Safety factor

Gerber uses the equation:
(Sm/Su)^2 + (Sa/Sn) = 1/N

Where Su = Ultimate tensile stress

and other variables defined as in the Soderberg equation.

I hope this is helpful.

RE: cyclic load on the agitator nozzle

Mr. Mathan,

Since you are dealing with a pressure vessel nozzle and head, I suggest you first look at Appendix 5 of the ASME Code Section VIII, Division 2. Appendix 5 contains fatigue analysis design criteria.

Vince Carucci

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