Welding 321 S/S Autogenous

[vanci]

I am having difficulty welding 321 S/S tube without any filler. I am consistantly being told it is due to a new low sulfur content. Also, that the Ti is bonding with another alloy which then becomes a lower eutectic point. The type of defect is porosity along the centerline of the weld. I believe it is due to cleanliness, and weld prep. Any advice would be appreciated!!

Thanks

 

[unclesyd]

Comeback with a little more information as to the size of tube and the method and welding parameters your are attempting to use.

 

[vanci]

We are using, TIG, Ar/He mix, approx. 90 amps, 20-30 ipm,.039 to .098 wall thinkness, this is a longitudinal seam weld.

thanks

 

[Goahead]

The standard advice is that 321 should never be welded autogenously because Ti, the preferential carbide forming element, whose function is to preserve chromium in the metal, is not going to survive melting.
Another objection is that by foregoing the use of filler metal one eliminates the possibility to introduce ferrite forming elements in the weld to prevent hot cracking.

http://www.welding-advisers.com/

 

[metengr]

AISI Type 321 stainless steel tubing is commonly seam welded because it is specified under ASME SA-249. This specification concerns welded austenitic stainless steel tubing that is welded with no addition of filler metal.

In your case, the cause of porosity in the seam weld is related to either a shielding gas problem or clealiness.

 

[unclesyd]

We made autogenous butt welds with an orbital welding machine in 321 SS tubing (1" 14 Ga and 1" 12 Ga). I just checked my notes and I didn't record any problems during welding or in service.

In line with metengr's comments when we first started autogenous welding (safe ending) of Hx tubes we actually used electropolishing techniques for cleaning in order to get a good weld.

How is the shape of the weld?
Is there any possible lubricant from the forming dies getting to the weld area.?

 

[vanci]

Thanks to all! I am glad to see my predictions are in line with the experts. I suspected that it was a cleanliness issue and/or gas problem. I am having the operator(s) clean the edges of the coil and am seeing better results, the plumbing system will also be checked this week. Thanks again!!