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Need advice on FEA results
2

Need advice on FEA results

Need advice on FEA results

(OP)
Hi,

The model being analysed is that of a lifting lug welded to the bottom ring of a support ring halfway up along the vessel.

In the FEA results I am reviewing, the overall von Mises stress plot comes out as 614.99MPa. The person doing the FEA then took a Stress Classification line at this spot through the thickness of the bottom support ring plate, and the membrane+bending stress came to 490.8MPa.

Now membrand+bending stress of 490.8MPa is less than 3 times S, with S being 173MPA (2/3 of the yield strength of SA-516 70), and thus passes.

My concern is the 615MPa von Mises stress. I am not sure of how to approach this value. The value seems very high, does it mean the analysis shows that the model will fail?

RE: Need advice on FEA results

The difference between the M+B and the total stress is classified as the peak stress (F). If the M+B stress can be classified as P+Q, then the interpretation is correct. Peak stress is only relevant in fatigue.

I would caution that classifying the M+B stress as P+Q may not necessarily be conservative for your specific situation.

Make sure that the SCL is "valid" per Appendix 5-A. Also, the current limit on P+Q is Sps, which is the greater of 3S or 2Sy.

RE: Need advice on FEA results

It is hard to say for sure without seeing the actual FEA setup and results. You could be getting false stress concentrations depending on how the analysis was setup. I agree with TGS4 in terms of the conservative aspect. When in doubt I usually go for the more conservative route to be safe. Also, where are you getting your factor of safety for the lifting lug. I recently had to design some lifting lugs for the company I work for (based in Alberta, Canada) and found that regulations dictate that the lifting lug not see more than 5 times the load it was rated for. So we had to use a factor of safety of 5.

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