Pipe geometry effect on fatigue cracking location of 90 degrees elbows under in-plane bending

초록

In this technical note, the criterion for fatigue cracking location for 90 degrees elbows under in-plane bending is presented. The criterion is found using published elastic solutions and elastic-plastic FE analysis results. It is found that the most important parameter affecting fatigue crack location is the mean radius-to-pipe thickness ratio, rm/t. The circumferential crack at outer intrados is predicted for r(m)/t <4-5, and the axial crack at inner crown for r(m)/t >4-5. The exact value of r(m)/t depends slightly on the bend radius-to-mean pipe radius ratio. This conclusion is found to be appropriate from high cycle fatigue to very low cycle fatigue loading, and to be independent on the material.

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