Hi all,

Currently we are performing stress analysis for the wellhead platform
We are also performing fatigue analysis because of the displacements caused by the waves in the ocean. (More than a million cycles during service span of paltform)

I am using 5-110-1A.FAT file for material fatigue properties for A106 Gr.B & A333 Gr.6.

I am not sure of the curve for B423 N08825 material. (I believe it should be one of the from 5-110-2A.FAT or 2B or 2C)

Please advice me on this.

Also currently I am performing static analysis for fatigue, do I need to consider harmonic analysis for this case?

Your reply will be highly appreciated.

Regards
Abhijeet Dhamapurkar
J. Ray McDermott Middle East Inc.

please reply

You need to consider a fatigue analysis using Miner's rule. Although you quote a large number of cycles, mostwill be associated with very small waves, probably causing stresses within the endurance limit. Dependent upon the sea area, typically waves in the 4 to 12m range induce enough stress with sufficient a numbers of cycles to cause fatigue issues. Look at your wave exceedance data and consider the stresses induced by displacements related to wave height.

There have been many posts on this subject, use the search facility.

I would not expect to consider a harmonic analysis for a wellhead. If there are harmonic problems predicted due to wave and current action, i.e. vortex shedding excitation on the exposed conductor tube, the design is flawed and needs more conductor guides.