Tig 2" sch 40 carbon ???

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Any suggestions on the best way to weld out 2" sch 40 carbon in 5G and 6G position?I welded 2G with no problems but in 5G I am having problems scorching my root with hot pass and filler and undercut on cap.  I am using 3/32 2%thor. tung, 1/8 gap, 1/8 filler, knife edge prep.  The root is good until hot pass and fillers put in.  I cool between passes, tried all types of amps with and w/o arc force.  Would 1/16 tungsten and 3/32 gap and filler be the way to go???
Reply:War Eagle,Given the joint setup you mention, I'd be running 85-90 amps for the root pass and 95-105 amps for the hot pass. Are you walking the cup  and laying the filler rod in the root opening to weld the root pass? If so, your weaving motion should be very narrow, about the width of the filler rod.  This focuses the heat onto the center of the joint.  Spreading the heat wider creates a wider root bead, and this wider bead is going to be thinner.  If you're feeding filler rod into the joint as you weld the root, you need to feed more metal; but only up to the point that your root reinforcement is still OK.A slight increas in heat for the hot pass is needed. but too much heat, combinded wiht too wide a weave motion, and/or too slow a travel speed will cause the problems you're describing wiht your root passes.Sometimes I'll knock the edge off of the bevel with a file, and this can help keep the root from spreading out too wide.  I'm not really talking about putting a land on the pipe, just enough root face that you can see the edge...like 1/64" or 1/32" of an inch, no more.  Takes about 2 light passes with a file to produce this.  Any more and you risk problems with lack of fusion on the root pass.  Try it once and see if it helps...For your cover pass, you can try a couple things.  First off, are you walking the cup on the cover pass?  If so, you need to concentrate the heat on the center of the joint.  The tungsten should stay parallel to the joint as you roll the cup from side to side.  Don't point the tungsten at the side of the joint.  As you move, let the puddle wash over to the side, don't push it their by pointing the arc at the bevel edge. Keep your arc length short so the cone of the arc is tightly focused, not broad.  All this will keep the heat focussed on the center of the joint, where you're adding filler metal, and not on the pipe to either side.  Adjust the amperage on the welder to accomodate heat building up in the pipe.  I can't tell you how much amperage to turn down, as this all depends on hot long you've been welding, how large the pipe nipples are that you're using for practice, and how fast you're traveling when you're welding, and a few more things besides.  If time isn't an issue, weld half the cap and cool the pipe back to room temperature before welding the second half of the cap.It's different than welding on say 6" schedule 80 pipe, where you have a lot of material to soak all the welding heat.  For 2" pipe you've got to keep the heat focussed on the joint.  Any time you're pointing the tungsten to the side of the joint, the heat of the arc is going to melt the base metal.  Unless you're really pushing the filler metal to the right place, you're going to get undercut.  Keep the filler metal on the center of the joint, keep the arc there too.  Use the right combination of heat and arc length to keep the puddle small; I'd guess the puddle shouldn't be any largeer than half the width of the joint at the surface of the pipe.  If you're moving the filler metal around to avoid undercut, you're going to wind up with a sloppy looking cap; unless you're a really skilled welder.See if any of this helps and check back if you're still struggling.  If any of this contradicts your instructor, you need to tell us what he's advising, so we can give advice that doesn't conflict.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:hey dab thanks for the quick reply.  I have been walking over the wire and trying not to hit the bevels hard when putting in the root.  I had good success early on root but on cap I was doing what you said not to.  That is trying to push the metal to far and it was looking ug-ly. I am using nipples anywhere from 4"-8" long each.  Even the longer ones didn't do much better.  I didn't get much help from the instructor on this just said go faster to keep the heat from building.  I am walking the cup on the cover.  Any practice beads I make on a clean piece of pipe of the same size are fine.  I use grinding disk and then sanding disk to  clean where it is shiny like new. I have been trying to use one bead cap with 1/8 wire I think I'll try 2 with 3/32.  Do you think smaller tungsten ,i.e.    1/16 would be advisable?  How about 3/32 gap and 3/32 wire for entire weld?  The wire is ER70S.thanks again,
Reply:3/32 tungsten is fine.  I don't think going to a smaller tungsten is going to solve your problem.  I was taught to run a single bead cap, as 2 beads takes twice as long; which the man won't like....I have used 3/32 filler for the cap pass, but stick with 1/8" for the root and fill.  Sometimes, if I let the arc length get too long, the 1/8" filler will form a big ball that always jumps to the point of my tungsten.  For some reason, I don't have this issue with the 3/32 filler rod on the cap.  With the smaller filler rod, if I let the arc get too long, it just melts away without forming a big ball that contaminates the tungsten.I meant to add that for welding in 6G, you're going to have to favor the uphill side of the joint.  Move the filler rod slightly above center and you can try pausing on the uphill side of the joint as you're weaving the weld bead.  This should help keep the weld bead even and not undercut the top side of the joint.If I remember correctly, it took me about 3 days to finally figure out how to weld 2" pipe in 5G position with TIG.  I thought I was going to never get it; but it finally clicked.  I went from welds that looked like rope wrapped around the pipe to nice smooth even beads.  Keep plugging away at it, and you'll get it too.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:You just saved me a trip to the welding supply.  I'll work on putting in a solid root, keeping the arc concentrated and parallel, and find the right heat and get er done.