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Difference between NB3200 and NB3600 regarding membrane/bending stress

Difference between NB3200 and NB3600 regarding membrane/bending stress

Difference between NB3200 and NB3600 regarding membrane/bending stress

(OP)

 I have a question regarding the definition of membrane/bending-stress in ASME NB-3200 compared to ASME NB-3600. My interpretation of 3200 is that the bending stress is the "thru wall thickness" bending stress. That is, if you apply a moment on a pipe you get mostly membrane stress and a small portion of bending stress thru the wall thickness. For example the allowable primary membrane stress in level A is Sm which never is more than 0.66Sy

 I get a little bit confused when I look at equation 9 in NB-3600 where the allowable stress is 1.5Sm which is Sy (if the allowable stress is based on the yield stress). For me this is not consistent with NB-3200. For me it would be more logical to limit the stress in equation 9 to Sm.

With this you could get a usage factor of 1.5 if you apply the limit of Sm (0.66Sy) for the primary membrane stress in NB-3200 on a pipe which is designed according to the rules in NB-3600. This seems too crazy to be true so I assume I´m a bit wrong here...?

Best Regards
tomas

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