Unsusual weld header configuration

[kclim]

We have a number of high temperature headers made from 2.25Cr 1Mo steel. They are stubbed with similar material. The branch welds connecting the two use a matching consumable although recent material identification suggests that the final weld run (on the stub side, furthest from the header) appears to be undermatched (1Cr 0.5Mo type consumable).

I'm guessing this was a mistake during manufacture. Perhaps it was initially welded correctly, but then they realised they required an additional run to be put down for compensation purposes, but grabbed the wrong consumable.

Or is there a better reason for this? Anyone care to comment?

Thanks

 

[blacksmith37]

Poor QC.
Long ago (drillings were taken for chem) a large number (25% +/-) of welds and base metals were incorrect in a new Cr:Mo unit (hydrogen),I guess things have not changed that much.

 

[metengr]

Your explanation is as good as others I can think of... one explanation is that the fabricator ran out of matching weld rod and decided to go with the next best option.

 

[Metaljon]

This does occasionally happen in plant construction. The welders pick up the incorrect rods for the job or get wrong documentation. We do PMI surveys on new plant construction and typically this happens about 1 in 100 welds.

 

[Mr168]

What method was used in determining the as-welded chemistry? I often trust PMI's of weld metal as far as I can throw them, particularly if it's been subject to PWHT.

 

[unclesyd]

Check your spool fabrication drawings to wee what was called out.