Our company is being required to make CJP-open root on 16" round HSS. The joint resembles a K section where two 16" diagonals frame into a 16" chord (top and bottom). It resembles the saddle-on geometry like what I used to see in piping branch connections. Our Production Manager has elected to use GMAW to complete the root and FCAW fill and cap. The majority of my personal experience is in SMAW and FCAW. Is there a tried and true selection of wire size, wire classification, gas mixtures, techniques (push vs pull), angles, etc. for this application??
Sounds like the hard way to do thing. But if your set on it, I would look at metal core.
I'm not sure I have a good picture in my mind... Can you give us a pic?
GMAW short circuit is used often enough to make open roots (without backing) on joints with lands with an approximate thickness no greater than 3/16..
100% Co2 provides greater penetration but can be prone to spatter if paramaters are not tightly controlled
75/25 Ar/Co2 provides a wider paramater range but slightly less penetration
0.035 solid wire with 17.5-20V WFS 180-240ipm are good for short circuiting open roots
A 10-15 degree drag travel angle will produce greater penetration with GMAW-S
Any type of spray transfer will be a bear with an open root, whether it's solid or MCAW (different gasses, wfs and Voltage apply also)
Lawrence,
I agree with what you state. I once worked for an outfit that had a couple of stud welders that could do a nice open root in spray (1G rolled). They would get it going so they could bridge the gap by using a piece of filler and feeding it into the pool almost like GTAW.
Mankenberg
AWS D10.11 "Root pass Welding of Pipe Without Backing, Recommended Practices" may be helpful.
Is this being done in the field? Is it roled out in the shop or is it welded in a fixed position? These two things play a huge role in what processes to choose.
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