Is it ok to weld a SA 234 Gr. WPB cap to a API 5L X 65 pipe?

[gbratis]

Here's a good one for you folks.
Is it permissible to weld a SA 234 Gr. WPB cap to a API 5L X 65 pipe? Our quality manager stated that if the calculated wall thickness is acceptable, they can be welded using of course a new WPS for this weld. Is this clause valid or I have to proceed with a gr WPHY-65 cap?
Thanks in advance.

 

[FIF99]

Hi,
With respect to welding additional measurements are expected to be taken, and indeed a new WPS/PQR should be prepared.
However, regarding the wall thickness I expect it is not possible. The WPB material is much weaker than the X65. On the welding end or taper zone the WPB material will most probably fail. It is uncommon to have a pipe wall selected in X65 with sufficient over-thickness suitable to meet sufficient wall thickness for the WPB fitting.
So, regarding the wall thickness you will have a problem I think.
Success.

Regards,
FKE

 

[metengr]

Your QA Manager is correct. The allowable stress is different between API 5L Grade X-65 pipe and SA 234 WPB.