Need help with Tig root, schedule 40 pipe 4" 2G

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I am currently in 4th semester of tech school welding program which is the pipe semester.  After making it through tig plate and now starteing tig pipe I am having all sorts of trouble putting in a root.  I have been running "pads" walking the cup and now have started on 4" sch. 40 2G position putting it all together.  I use a knife edge, 3/32 gap and 1/8 filler and 1/8 2 % tung.  I have tried lay wire method, with about 90 amps.  Maybe I just need more practice.  What is a proven technique that will work with a good or bad fitup.  I have heard of back feeding the wire and also laying the torch back and feeding the filler wire at a 90 degree angle to each other(keyhole).  As you can tell I have got a lot of information but don't know what to use.
Reply:You nreed to use what works or you are most comfortable with. After that, you can experiment with other techniques.Have a nice dayhttp://www.weldingdata.com/
Reply:What sort of problems are you having?
Reply:I would have to agree that some more info and some pics would be great tools for us to help you.
Reply:For myself I do not like to use a knife edge, I can tell you what I use and what works for me and you'll have to experiment for yourself.Tungsten: 3/32" diameter 2% thoriatedShielding gas: Argon 15-20 cfhCup: I prefer a #7 using a gas lens but use a #7 with a collet body just fine as wellAmperage: I prefer to use a foot pedal to have complete control of temperature but when using scratch start or lift arc I set the machine to approximately 75 ampsFiller Rod: I use a 3/32" diameter rodJoint Set Up: I like to leave a 1/16" land minimum and prefer a 3/32" land. I find if I do not leave a land the internal bead will easily become concave. The edges burn back quickly leaving too large of a root opening. This becomes especially difficult to control if you are not using a foot pedal to control your heat.I tack the pipe in four locations using a 1/8" filler rod as my spacer. I make the tacks approximately 1/2" in length. I like to use a 3/32" thick grinding wheel on my angle grinder to feather out the start/stops of my tacks to allow for the final weld to blend in smoothly.With a slightly larger gap I find that when welding I can slide the 3/32 filler wire right into the root opening and add the filler wire into the root easily.  With a thinner gap I find that the rod tends to want to sit on top and you need to use more heat to open the keyhole to allow the wire to penetrate. I use a free hand technique ( I don't walk the cup) for my roots. This has always worked well for myself, I hope that it will work for you as well.RegardsER70S0-2P.s. Please describe the issues that you have had with your roots, Lack of Penetration, concavity, etc ?
Reply:Thanks for all the advice and also let me try to answer all replies in one shot.To start most of my problems are from suck back (concavity of the root).  I have been told that by my instructor.  Occasionally I will have a knot from my filler wire pushing through and building up. Here is my set-up:  1/8 tungsten, 1/8 gas lens , #6 jumbo cup, 1/8 inch tungsten stick out or close to reaching inside pipe when held straight in, knife edge, 3/32 gap, 1/8 filler wire 100 amps, air cooled 17v torch scratch start.  I don't really walk the cup just wiggle the width of the wire along the wire laying in the gap.    I did run a root that was somewhat better today with 1/8 gap and 1/8 wire.  Sorry I don't access to camera or ability to post pictures on the forum.  Everyone has there on way I guess am my instructor is very knowlegeable but his method is not working for me.  ER-70s-2's description of how he put his root in will be attempted tomorrow.  I know it takes practice but I want to have a tried and proven method that will work in most all situations and even if it takes longer to learn in the end when I get in the field I will be able to cover most situations thrown at me.  One other question when feeding the wire in the bevel should the wire be resting against the bevel (wire width inside from the back of pipe) or should it be held with 1/2 of the wire still on land and bevel and the rest inside the back of the pipe (hope that makes sense).
Reply:100 amps is too hot.  Keep your side to side motion(or up down in the case of 2G) narrow.  If you go too wide, you'll melt too much base metal, which can give you suck back unless you realize it at the time, and push a bunch of filler into the puddle.  Of course, this is hard to do, and if you push too much, then you end up with excessive root reinforcement.Keep that arc length very short and focused on teh puddle.  Don't weave wider than the root opening.  Try to run about 85 amps tops.  This should be more than enough heat if your arc length is short, <1/16", and your weave is tight.Benson's Mobile Welding - Dayton, OH metro area - AWS Certified Welding Inspector
Reply:thanks a dab will do.  does that mean running 1/8 tung., 1/8 wire 1/8 gap? also how far do I need to put the wire when I lay it on the bevel inside the pipe?
Reply:Good luck tomorrow and I hope you have success with the method I use. As to your last question, I like to feed the rod right into the root(the rod is basically fed right in between the lands of either pipe, this can be done with a 1/8" root opening and a 3/32" filler wire as you have the room to manipulate the filler as needed). In my mind I'm feeding the filler into the area where it needs to be, into the root.  One suggestion, try a little more stick out on your tungsten so that you can maintain a tight arc as "A Dab Will Do" suggested. With only 1/8" stick out the cup is going to be resting on the pipe to get close enough to properly control the puddle. I would guess that you are probably heating up too much of the bevel and melting that down into your root as well. If you don't mind, try at least 1/4" stick out to 3/8". Your using a gas lens so coverage will be good, as well your tungsten is down in that bevel so contamination should not be an issue. You'll be able to get the tungsten down into the root where you want it and you'll be able to control the arc much better....as well you'll be able to see your tungsten.  Just ensure you have enough post flow to prevent the tungsten from turning black after the arc is extinguised. One other thing, try a 3/32" tungsten if it's available, for the heat you are using 1/8" is overkill. You'll find the 3/32" will give you that much more room to manipulate it, or grind a long narrow taper on the 1/8" to make it more like a 3/32" tungsten.  A root in pipe is always more difficult then plate. I remember the first pressure vessel company I worked for. I passed the plate test no problem, then on the first job I had to put a tig root in a 48" diameter shell to a head......it wasn't pretty to say the least. After watching one of the senior guys do it I learned tand practiced the techniques. Witha little practice you'll have this nailed down in no time.Er70S-2
Reply:ER70  that all helps tremendously.  Will this work on 5G and 6g?  also is back feeding wire from inside something that needs to be picked up? thanks
Reply:Yes, I use the same technique for all positions. How you feed the filler will be something that you need to develope yourself. Personally I always dab the wire onto one side of the root opening and then move the torch to wash it across to the otherside of the joint.You're going to take a little from what I have said, a little from another person etc etc and eventually you will develope your own technique that works for you. Welding is a very personal thing and we all have different hands. Just remember, welding is all about manipulating a molten puddle of "steel" and making it do what you want it to do. Take your time and don't be afraid to try new things, follow your gut instincts. It's not rocket science, if I can do it then you certainly can. try to watch others, that's the easist way to pick it up.RegardsER70S-2
Reply:ER 70  you nailed it on the head.  I try to gather all the info I can and put it together thru practice and practice and practice.  even though my stick roots are far from perfect I am treating my tig roots the same way and with enough time under hood I will keep on until they are passable or better.  Thanks for your time and advice. (Thanks to other replies as well) war eagle
Reply:I use 3/32 ceriated tungsten, but it can be done with 1/8" as well.  I like 1/8 wire for the root and fill passes.  I have had better luck capping with 3/32" filler.  For me it makes for a flatter bead and easier puddle control.  But it's harder to keep from melting ahead too far, so your arc length control needs to be rock steady.I like a tight 1/8" root opening, 0-1/32" root face.  I file just enough to knock the burrs off.  The filler should not fall through the root opening.  If it does, angle it off to one side or the other, just enough to keep this from happening.  Which side doesn't matter in 5G, I'd point it at the top bevel for 2G or 6G welds.  In perfect conditions you should 'consume' or incorporate the filler into the puddle as you move the arc forward along the joint.  In reality, you may need to move the filler in or out of the puddle, depending on a whole bunch of variables; like arc length, amperage, heat accumulated in the base metal, etc. Originally Posted by war eagle 81thanks a dab will do.  does that mean running 1/8 tung., 1/8 wire 1/8 gap? also how far do I need to put the wire when I lay it on the bevel inside the pipe?