Cracks on SA213TP347H Tube surface

[erhari30]

Branched Crack was identified for about 80mm length with zig-zag pattern on Dissimilar welded tubes
between S213TP347H to SA213T91; The crack had branching exactly 3 lines seperated by 120 deg at an
isolated distance of 25 mm; All were joined by a continuous line (which revealed in LPI examination)

One side of crack was originated from HAZ on 347H side and crack runs on 347H side for about 80mm length.

JOB: Superheater coil
SERVICE : NOT PUT INTO SERVICE/UNDER MANUFACTURE STAGE
PWHT: Local Stress Relieving by Resistance method done
Hydro Test at 450 KSC for 5 minutes completed

CRACK WAS OBSERVED DURING VISUAL EXAMINATION

Please throw more light on the root cause for such crack on 347H material.

 

[davefitz]

I think you would need to add some more information, such as the weld filler and weld procedure.

"In this bright future, you can't forget your past..." Bob Marley

 

[metengr]

Cut the tube section out and have a proper metallurgical analysis performed. The root cause of the DMW cracking could be from improper welding technique to stress corrosion cracking to defects in the tube material. Trying to assume or guess is worthless without this analysis.

 

[EdStainless]

Welding 347H can be interesting. If it is stabilized before hand there will be a zone near the weld where it becomes re-solutioned. Now add to that the dilution in the weld from the 91, and you understand why we have a hundred questions.
Cut it out and have it properly analyzed. It might be worth it to give the same lab your qualification weld sample. There may be lessons to be learned.

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P.E. Metallurgy, Plymouth Tube

 

[weldstan]

I have seen similar welds fail in less than 10 thermal cycles. I would not recommend this direct dissimilar joint without a transition piece.
Agree with the above recommendations from weldengr and Ed.