question for experienced stainless pipewelders.

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Ive welded a some smaller diameter stainless pipe. sch.40, 80. and the fits usually were pretty good.  Usually the root gap would be 1/8 to 5/32. and on the root ive been able to backfeed, keyhole it, or walk the wire with success using 1/16, 3/32 to 1/8 wire. Ive put a lot of roots in carbon from one inch up to 36'' with success also.  Being that a lot of my welding is done in the field in position, On the fits that have a lot of hi-lo or id mismatch, ive been feeding my wire from the bevel thats deepest in the root  and working it to the shallower bevel, to make sure i break down both bevels. Ive learned that just walking the wire on a root is not possible in a lot of situations, because a lot of time the fit is not going to be the same, you end up with a tight gap, a wide gap hi lo, etc.  On a lot of the stainless roots i ran they were like 3'' with perfect gaps id start with a 1/8 gap, and lay the wire on the bevels an just walk over the wire and my method was working,to get a decent root in. but ive never put a root in a bigger stainless pipe. So the other day at work I got to work on a 12'' stainless line, i think it was sch.80, it was tacked up by someone else. the weld had a nice gap over at least and over 5/32 all the way around, but stainless does pull and i thought i was fine with that. so we set up and purged the line, checked the purge with a meter, got it under 2% o2. I set my machine to 90 amps, used a gas lense and #8 cup with a 1/8 tungsten, and 1/8th ER308L wire. i immediately had trouble feeding the root. I tried to backfeed it like i would have carbon, but it didnt want to penetrate the inside bevel.. my welding partner, (who has that superwelder attitude) showed me how he runs his, he said he keyholes his and feeds his stainless from the shallow bevel to the deep. i tried this method also, but ended up with a lot of grinding also, so basicaly i let him run the root and then we filled it up.Ive always took all the advice i can get to help my skilll, so any advice on running a stainless root, on something with a bigger gap and high low.
Reply:On bigger s.s. pipe I use a 3/16" gap and usually start with a 5/32" wire, backfeeding it. By the time you get to the top or last quarter a 1/8" wire will fit the gap just right. With the purge I'm a lil oldschool I just go by the feel of argon flow on back of my hand.Last edited by slim83; 02-25-2011 at 09:41 PM.
Reply:What about dealing with a  fit up that has hi lo.
Reply:A bigger gap with the bigger fill rod tends to help with hi lo imo. I also will run a grinding disc once I get it tacked like I was grinding a bead on carbon keeping disc on the side that's lower. That tends to thin the lower side out make for a better tie in and better weld. I've dealt with quite a lot of bad fits on stainless and just taking the extra time to make a good fit is the best thing you can do. I know sometimes that the big stainless is just so damned egged hi lo is impossible to avoid. Patience is a virtue wheen working with stainless. Keyholing also works well but I don't like the way the bead looks when keyholing
Reply:Thanks for all the tips.