DMW

[akvtech]

Other threads have approached the subject and in my case a client used 309 filler metal to weld about 25 different 316ss Thermowells in crude and reformer sections of their refinery. Some lines are CS and others are 1-1/4cr and 2-1/4cr. They have lots of cracking issues after startup and first few weeks of run time. Service temps are from 400°f to 675°f.
I suggested they replace and use Inconel 82 ErNiCr-3 and Inconel 182 ENiCrFe-3 filler metal across the board to be safe.

They asked if there is any data supporting the use of 309 filler in this application. In the CS maybe at the lower temp ranges?
References and advice is appreciated

 

[metengr]

If you had this short of run time and leaks, this sounds like a weld quality issue (lack of fusion, underbead cracking from low preheat). I do agree with using Inconel at service temperatures at or above 700 deg F because of carbon migration problems associated with DMW's.

 

[btrueblood]

Sorry to be a pest - what does DMW stand for? I assume Dissimilar Metal Weld, but you know how assume is spelled...

 

[DVWE]

Is there a main welding process used (SMAW, GTAW, etc.)? And are the welds tested before being put in service?

 

[akvtech]

Yes DMW is Dissimilar Metal Welding.
GTAW and SMAW
Like Metengr said technique is likely as much the culprit as anything. Does anyone know when the temp limitations on DMW with 309 came about?

 

[metengr]

On the job experience and looking at many DMW failures over my short life span where carbon migration along the weld fusion zone resulted in local creep failure.

 

[stanweld]

Assuming that some, if not all, of the dissimilar metal welds required Code mandated PWHT, it has long been the practice to make such welds with Nickel base alloy welding filler metals.