The B31.3 code distinguishes between in-plane and out-plane because fatigue failure on Markl's tested components indicated so. If I have an elbow with an in-plane SIF=3 and and out-plane SIF=4, then the elbow fails due to in-plane bending with 1/3 the bending moment it takes to fail a girth butt weld at the same number of cycles. Likewise in my example, only one quarter of the same moment is needed to fail out of plane. Component geometry is the key.
There is no reason to fret over some fancy 3D component as it is not in Table D-300. Markl didn't test it and the code does not define stress indices for it. In the past this meant running your own test although these days FEA serves this purpose well. Tony Paulin's software estimates these values.
B31.1 does not distinguish between in- and out-plane.
Keep your focus.
Dave Received on Fri Jul 02 10:17:00 2004
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