Weld Cracks on SS to CS Wels

[Kunal88]

Dear All,

I am facing an issue on the propagation of cracks on a dissimilar metal weld. The cracks happened in three different scenarios
There is element holder bearing MOC as SS304 which was welded to SA516Gr70N shell. Due to code requirements the vessel was subjected to PWHT.
There was a crack propagation in the weld and the crack was noticed in the following conditions
1) Crack in element holder to shell weld after PWHT.
2) Crack in element holder to shell weld after Hydrotest

I would like to know the reason of this crack development and how to arrest the same.

Regards
Kunal Duggal

 

[DVWE]

More than likely it was the difference in the coefficient of thermal expansion between the two materials that caused the weld cracking.

The devil is in the details; she also wears prada.

 

Call in an expert to perform a root cause failure analysis. These questions are not answered by crowdsourcing.

"Everyone is entitled to their own opinions, but they are not entitled to their own facts."

 

[meltedEng]

^ I agree.

You have too many variables that might cause this, that are very relevant:
Joint type, thickness, filler metal, process, interpass, preheat, PWHT (1650 for 2 hrs?)

Did you UT/RT/LPI prior to any treatments or confirm the weld was good prior? The suggestion of differential thermal expansion is a good one, what do the calcs say? Is it restraining? Maybe you are better off to butter, then attach.

 

[MJCronin]

Your reason for crack development was the MBA who allowed the welding of 304SS valves onto the Carbon steel shell ....

You would have no problems with this type of joint if it were a flanged joint between the Carbon steel and SS...

MJCronin
Sr. Process Engineer

 

[weldstan]

Whereas Code (ASME VIII?) required PWHT (1100F min) of the shell due to SA-516-70 thickness, the dissimilar attachment weld may not be subject to Code PWWHT requirements. Regardless the filler parameters discussed by meltedEng have not been identified so how do you expect an answer to your question?