Fatigue Analysis
Fatigue Analysis
(OP)
ALL,
I need to a basic fatigue analysis on Vessel nozzles using PD5500 using SN curves. Do I start with the Stress range, Sr, and then get the no. of cycles or do I calculate the no. of cycles and then get the allowable stress range from the curve?
Ultimately I require a suitable thickness of vessel for a given series of stress cycles ie 4 different stress ranges at 4 different no of cycles.
All help appreciated,
Cheers,
JohnOD
I need to a basic fatigue analysis on Vessel nozzles using PD5500 using SN curves. Do I start with the Stress range, Sr, and then get the no. of cycles or do I calculate the no. of cycles and then get the allowable stress range from the curve?
Ultimately I require a suitable thickness of vessel for a given series of stress cycles ie 4 different stress ranges at 4 different no of cycles.
All help appreciated,
Cheers,
JohnOD





RE: Fatigue Analysis
If the allowable number is too small you have to change the design.
RE: Fatigue Analysis
You may have available some other degrees of freedom. For example , if it is a thick walled vessel, you might be able to define the allowable rate of change of vessel temperature in order to limit the thermal stress for a specific type of cycle.
Also, if there are 4 different cycles and they are imposed in a random manner , then you might be able to calculate a smaller total life consumption by using the rainflow cycle counting algorithm ( use a monte carlo simulation for the sequence of cycles).
There is a good summary in the EU PED standard EN-12952-4:2000 app B