Another Sub-Arc Girter question 1

[OSUWE2010]

We are using a single wire SAW tractor with L-61, 5/32" wire, Lincolnweld 980 Flux to weld up some 1.5"-2" thick girters. We're using a double-bevel groove weld (TC-U5-S) but the customers want us to do this without backgouging, so this becomes a procedure we need to prequalify, correct?? Any tips on settings or procedure for doing this and has anyone done this before? Any help is greatly appreciated.

 

[dhengr]

Who designed the weld and the joint detail? How is it stressed and loaded, and how highly is it stressed? Do they really need a full pen. weld, or would smaller bevels or even two fillets work? If this is a flange to web weld, it seems that many people mistakenly assume that since a rolled WF beam is solid steel at this flange/web joint, all plate girders or built-up girders must be too. This is rarely the case. The fact is that many (some percentage) of the larger rolled sections have rolled-in defects (inclusions, piping and the like) at this very location, similar to what would occur if you didn’t backgouge the double vee groove before welding the second side. Ask them why they don’t want you to backgouge before the second weld, it just may not be needed, but then the full bevels probably aren’t either. I’m not saying this complies with AWS, or advocating doing this, but with SAW the penetration is good enough that the second side weld probably boils any problems out of the root of the first side weld, when the root face is small.

If they really need a full pen. weld, then backgouging is more than likely needed. This might be the case on a flange plate splice which is highly loaded, perpendicular to the potential defects. But, then you have the wrong weld joint designation. And, I would most likely UT this weld after completion.

 

[weldtek]

Full pen without back gouging is certainly achievable but in my experience it can be a source of frustration as well.
Since you're using Lincoln products I'd suggest you get with their technical department for suggestions on welding parameters. Once you have those, things like joint geometry, land thickness, fit up and wire placement are critical.
Two methods I've used are, 1. a flux backup which typically requires some additional equipment, and 2. careful choice of joint details, fit up and welding technique.
You have to consider that with the latter method wire placement is absolutely critical. If the wire is off one diameter, which isn't much, you may lose the required penetration and with a tractor,it's easy to move off the mark.