Fatigue analysis with pressure fluctuation only 1

[jtseng123]

Dear all,

I have a drum with temperature in conctant, but pressure changes in a cycle from 200 psig to 50 psig, then back to 200 psig.

Vendor is using the pressure difference of 150 psig to run the Von Mises stress, then based on Div 2, Eq 5.29 to calculate the stress range and then determine the fatigue cycles.
Questions:
1). Is it correct just by using pressure difference for fatigue analysis ?
2). Is it correct just by using pressure difference to calculate pressure thrust acting at the nozzle?

 

[TGS4]

Provided that there will be no stress reversals and the analysis is linear-elastic, then such an approach would be acceptable following the principle of super-position.