Allowable stress Copper nickel seam welded pipe ASME SB-467, ASTM B467 (C70600, C71500)

[sjrfc2]

I'm trying to find out why there are different allowable stresses for copper nickel piping above and below 4.5" outside diameter. Plate allowable strengths (eg B171) seem constant so I'd think that the allowable stress of the pipe, if made from plate, should be the same if a constant efficiency is assigned to the seam weld.

I'm struggling to find the basis of it and am assuming it has something to do with the manufacturing process since it's based on size. If someone could point me in the right direction to determine the reason I'd appreciate the help.

Thanks

 

[EdStainless]

Did they follow the same rules as with SS and the welded pipe is 15% below smls?


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