Dear Experts,
As you are aware that clause 302.3.5 (e) of ASME B 31.3 recommends the use of weld joint strength reduction factor "W" for design of longitudinal and spiral welded piping components. But for circumferential welds ( at butt ends weld joints) it has been put on shoulders of designer.
Now here i want your expert opinion that for seamless pipes should we consider this factor to take care the circumferential weld joints specifically at field or shop ?
In one of our project for 30" seamless SS 347H pipe material (temperature around 650 deg C) our recommended thickness was around 45 mm but the fabricator or client has considered this "W" factor and the thickness went to 65mm. Now after the operation of around 1 year, cracks were observed at circumferential welds.Surprisingly cracks were also seen at locations of fillet welds for pipe supports.
Initial investigation suggest that it may be due to stress relaxation cracking. As you know that thicker pipe mainly stabilized stainless steel are more prone for stress relaxation cracking.
So here the consideration of weld joint strength reduction factor in thickness calculation was ok ? As far as i think, its not required . Even if client or fabricator anticipated high stresses at these welds, than while evaluating longitudinal stresses for sustained loads at circumferential welds the allowable stress Sh should be adjusted by multiplying it by W.
Please share your views
-- As you are aware that clause 302.3.5 (e) of ASME B 31.3 recommends the use of weld joint strength reduction factor "W" for design of longitudinal and spiral welded piping components. But for circumferential welds ( at butt ends weld joints) it has been put on shoulders of designer.
Now here i want your expert opinion that for seamless pipes should we consider this factor to take care the circumferential weld joints specifically at field or shop ?
In one of our project for 30" seamless SS 347H pipe material (temperature around 650 deg C) our recommended thickness was around 45 mm but the fabricator or client has considered this "W" factor and the thickness went to 65mm. Now after the operation of around 1 year, cracks were observed at circumferential welds.Surprisingly cracks were also seen at locations of fillet welds for pipe supports.
Initial investigation suggest that it may be due to stress relaxation cracking. As you know that thicker pipe mainly stabilized stainless steel are more prone for stress relaxation cracking.
So here the consideration of weld joint strength reduction factor in thickness calculation was ok ? As far as i think, its not required . Even if client or fabricator anticipated high stresses at these welds, than while evaluating longitudinal stresses for sustained loads at circumferential welds the allowable stress Sh should be adjusted by multiplying it by W.
Please share your views
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