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UW12, Welded Pipe & Combined Loading

UW12, Welded Pipe & Combined Loading

UW12, Welded Pipe & Combined Loading

(OP)
Hi all,

we have a vessel design here that is failing in combined loading from wind and seismic action.

It is SA-312 TP316L welded pipe. But unfortunately the purchaser did not specify radiography on the pipe so we have no record of that for the longitudinal seams (2 seams 180° apart on the shell).

following on from both UW-12(d) it is my understanding that we treat the pipe as a seamless pipe but apply the welded pipe allowable stress value from Section II. This equates to 85% allowable stress of the seamless version. But then since we dont meet the requirements of UW-11(a)(5)(b)(as we have no RT cert) we use E=0.85 for our Cat A longitudinal weld.

Therefore in our calculation for UG-27 we are effectively using double joint efficiency (0.85*0.85 = 0.72) against the seamless pipe allowable stress value for the longitudinal seam.

But if we meet the spot requirements of UW-11 and increase our E to 1 (1*0.85 = 0.85) by radiographing the longitudinal seams , can we then use the seamless stress values from section II.

Essentially we need to use the seamless stress values to overcome the bending stresses which are about 5% above the welded pipe values.

I have a feeling that we cant do this but i was looking for some others input in this as the 2 designers in the office here are at odds on the situation.

Thanks

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