GTAW Pipe Large gap help....

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Need HELP>> lolWhat is the best way to handle a large gap in a pipe with GTAW? I was also wondering about backfeeding the tig wire from inside the pipe. I'm not sure of the technique? Do you look inside pipe gap from top & and watch the wire and hold torch underneath?I'm asking this because i'm a amateur at gtaw on pipe. I've been welding 9yrs and Tig about 3 months. Well I got the bright idea the last job I was on, to come in as a combo welder instead of structural welder. Well I passed the 6g test 2in sch 160 Tig & 2in sch 160 Tig & Stick. Well, I got on the job and welded a 20in that had about 3/16 to 1/4 gap, basically it screwed the root and got ran off. I just can't handle a large gap, I fit mine at a 3/32. Well, before they pulled my stencil, they asked me why i didnt feed it from the inside. Which I don't know how to do.
Reply:The old saying "Two wrong's don't make a right" comes to mind.I've fed the rod from the inside, when needed, for the past 25 years. Usually it was because of a bad fit up or getting moved to another area where the fit was made by someone else.Every welder has a different technique. I usually feed some extra metal inside the pipe and run hot enough on the second pass to blend in the extra without sucking it out.I have worked with welders who fit up a wide gap and feed from the inside on every weld.Some of the issues when feeding from the inside are 1) If your rod sticks, it will leave a blemish that must be re-consumed, 2) You are opening up another hole for your purge gas to escape or let air into the pipe, 3) It's a "one shot" method and trying to save an imperfection, it is difficult.The joint gets much warmer when feeding from the inside rather than feeding in on a narrow gap. Just more to deal with. That increases your chance of suck back.It's like other things with welding. If you want to get good at feeding from the inside, it's going to take practice.Good Luck,HoboLincoln SA200's... at least 15 - 20. They come and go. Growing partial to the "Short Hoods" in my old age. Last count on Short Hoods was 13 in possession.
Reply:a) If your fit sucks that bad, odds are you're not in compliance with the applicable code and WPS, though 3/16" is more than doable.b) Start by welding the narrowest parts of the root first, so that it draws the gap shut.  Your options from there are to lay your wire back and feed from the back side of the puddle (i.e. the wire will take a shortcut through the ID of the pipe so you're essentially using the solid wire to help support/bridge the molten puddle), or to go to a larger diameter wire (we usually keep some 5/32" stocked on the sites as a just-in-case.)
Reply:Well, you are right about someone fitting it, lol I was pulled off a 6in pipe to weld that 20in, they said  don't worry everything is already up there, you don't even have take your Tig rig up there, just use the other guys thats already there, its ready to go just weld it out. hmmm... well i kinda see the f**ing i got, I had to cut TWO 5/32 pieces of wire and hold them together and it falling through in places STILL.Thanks for the help, I'll have to practice the backfeed and learn to stick it to em and tell them close it up or i'm not going to strike a arc on it.
Reply:On large gaps I swing the root wide and feed all my filler on the sidewalls.Don't add metal in the middle it will take care of itself. I also prefer smaller diameter filler as it consumes more consistent if that makes sense. Just did 68 welds 100% x-ray 2 1/4" tube .330 wall and all had nearly 3/8" gaps on the bottom as some bending was off and all were one shot welds.I used 1/16" filler but on 20" pipe id be thinking along the liñes of 3/32" filler.Hope this helps.