ASME B 31.3-Weld Joint strength reduction factor "W" for seamless pipe ?

[ATUL KHATRI]

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

 

[XL83NL]

I think you provided the answer already, it's up to the designer. But to get the discussion going, and maybe gain support from other engineers (more) familiar (than me) on this topic, Ill throw in the first hints;

http://proceedings.asmedigitalcollection.asme.org/proceeding.aspx?articleid=1570634

http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=69829

https://www.littlepeng.com/single-p...ound-on-Weld-Joint-Strength-reduction-Factors

http://forums.coade.com/ubbthreads/ubbthreads.php?ubb=showflat&Number=67052

 

[ATUL KHATRI]

Thanks XL83NL

As far as I understood ,for seamless pipe ,weld joint strength reduction factor should not be used for wall thickness calculation. Use of “W” will unnecessarily increase the pipe thickness and weight which will induce more stresses at circumferential welds. If the designer or fabricator anticipate significant sustained stresses at circumferential welds than proper supporting of that pipe shall be done to ensure that the generated stresses are considerably lesser (here he can multiply the “W” with allowable stress to get new allowable stress ) than its allowable stress.

I will update on this matter if something else will come to my knowledge.

 

[XL83NL]

You may also want to get a copy of ASME STP-PT-077. It might contain some useful information for your specific problem.