Hardwire Root Pass
Hardwire Root Pass
(OP)
I am looking for a process to substitute GTAW in welding pipe (root). What is the fastest hardwire process that will give adequate results? I was thinking STT (surface tension transfer) would work, but was wondering if there was a better process. I am looking for more speed, without sacrificing quality.
Thanks in advance.
Thanks in advance.





RE: Hardwire Root Pass
For 'Position' welds, Pulsed GMAW is fast and 'trustworthy'. No risk of your weld turning into a braze. And it can be VERY fast, assuming a good, uniform fit-up with a uniform land on the root face.
RE: Hardwire Root Pass
There is a lot of hype by Ed Craig, but he knows welding, that you will have to read through. Ed likes his soap box, the good thing is he can backup what he says.
http://www.weldreality.com/TIP-TIG-welding.htm
RE: Hardwire Root Pass
RE: Hardwire Root Pass
We were doing heavy wall carbon and chromolly pipe welds with Lincoln STT machines in rotators 15 odd years ago and they were brilliant.
Unlike GTAW set up where a good clean, uniform root setup was critical the STT was very forgiving.
If you had a bad fit-up - 1 mm root in places up to 4 mm in others (definitely 4 mm maximum) we would just knife it with a 3.2 mm cutting disc and then weld. No need to clean the swarf out of the inside of the pipe - it was picked up by the molten root.
GTAW quality root runs at about 1/4 the time.
Regards,
Kiwi
RE: Hardwire Root Pass
RE: Hardwire Root Pass
GTAW manually feeds a stiff wire into the melted puddle, so there is (seldom) any wire "stub" left sticking out of the weld. Those that do occur (wire stub or electrode sticking) are very visible, are ground off, and the welder restarts - usually with a freshly ground electrode.
When the root gap on a pipe-pipe weld prep or pipe-fitting weld prep is larger than the wire dia - and this will almost almost always be the case - then the initial "feed" of the wire can get aimed into that root gap. The wire goes into the gap, the welder slightly moves has hand or position just a little bit, and the arc starts up. But the first 1/2, 1, or 1-1/2 inches of wire are already into the inside of the pipe before the arc melts off the wire and the puddle starts up back in the prep area between the two pipes. The stub length of wire is left inside as the start of a plug, or flow trap, or OFD material inside the pipe invisible to the inspectors and cleaners later on.
If EVERY weld and EVERY arc start point is begun by "aiming" the wire directly into the angled wall of the pipe prep area, then this wire stub is immediately melted when the air starts and there is no remnant left inside the pipe. But that degree of care in starting of every weld arc is very hard to verify.
If you begin this weld process, boroscope every pipe after fabrication of the next piece and before flushing and QA to look the stubs and wire traps inside every pipe. Removal of the stubs inside, and of the broken off stubs and grinding grit after they get ground off inside can be very difficult.
If you do the root pass with manual GTAW, then fill out the welds with wire feed, no wire stubs can be created inside the pipe, but then you need a slower root pass.
RE: Hardwire Root Pass
RE: Hardwire Root Pass
Once recognized, the problem is half-solved.