Hi all As per client specification

[rajeev383]

Hi all
As per client specification
"since the zero crossing periods of the cyclic load are less than 25 seconds for most equipment on this FPSO, the total cycles in 25 years exceeds 30X10^6, therefore fatigue analysis is required"???
Can any one please provide me the procedure to calculate the fatigue analysis of pressure vessel?
thanks in advance

 

[BenStewart]

What's the vessel design code? A new or old vessel? What is the actual zero crossing period, it can vary quite a bit depending on location and over 25 years can change the number of cycles considerably.

You'll need to consider all the acceleration loads on the equipment and consider stress ranges from, for example, bending around the saddles or skirts, cyclic piping loads on nozzles etc.

Suggest looking at the original design code and then DNVGL-RP-C203.

If going down the so called "Weibull approach" particular consideration to which largest stress range and Weibull shape parameter should be selected. For example, cyclic nozzle loads are going to be influenced by any pipe support friction. If using the maximum loads/accelerations (to calculate the maximum stress range) these are likely to overcome the frictional effect but lesser loads may not overcome friction which may be worse from a stress range and fatigue perspective.