[Guido_fairtown]

I've been welding for a few years, mainly stick, but I've been tig welding for only few months now. I've got it down pretty well though, can pass X-rays on carbon pipe, and sch. 40 stainless pipe, but I'm having some major problems with sch. 10 stainless pipe, mainly with getting the root in there nicely and PIPE DISTORTION AND BOWING. I usually run the same gap and wire - 5/32 gap and 3/32 wire (308 usually), with 4 tacks about 1/4" to 1/2" long (I've only been testing on 2" and 3" pipe). On carbon I do the same thing but run 1/8 wire and it goes in beautiful. That's the long and short of it right there pretty much, I need some help...

[Rick_H]

I've been welding for a few years, mainly stick, but I've been tig welding for only few months now. I've got it down pretty well though, can pass X-rays on carbon pipe, and sch. 40 stainless pipe, but I'm having some major problems with sch. 10 stainless pipe, mainly with getting the root in there nicely and PIPE DISTORTION AND BOWING. I usually run the same gap and wire - 5/32 gap and 3/32 wire (308 usually), with 4 tacks about 1/4" to 1/2" long (I've only been testing on 2" and 3" pipe). On carbon I do the same thing but run 1/8 wire and it goes in beautiful. That's the long and short of it right there pretty much, I need some help...

What settings are you using? What is your torch setup? Are you purging, what cfh?

I assume 2 passes?

[Poland308]

I like as little gap as I can get away with and still get a good root. Sch 10 likes to pull together a lot. Some times you can watch your gap close completely by the time you have the root half way done.
Like Rick said info on weather or not your useing an internal purge and what kinda amps.

[Guido_fairtown]

Around 50 amps on a miller dialarc. Tig torch - Weldcraft w-17 flexhead with a number 10 cup, 1/8" tungsten. Argon purge at about 8-10 cfh.

I start by putting a somewhat steep bevel on the coupons, (6g position) then i tack, square, repeat. Then i start running my bead at the bottom (6 o'clock position) and run up to my first tack (9 o'clock position). I then go back and start at the 6 o'clock position again and run up to my tack on the other side at the 3 o'clock position. Then i jump back over to the other side and start on my tack at the 9 o'clock position and run up to the top tack at the 12 o'clock position. Then i go back to the other side and start on the tack at the 3 o'clock position and run up to the top tack at the 12 o'clock position, completing the root. But when im done, the pipe is usually bowing and im not always to happy with how the root is looking especially my tie-ins to my tacks.

[Poland308]

Try moving your tack on the bottom to a 7 o'clock position and then start welding at 6.

[Guido_fairtown]

Try moving your tack on the bottom to a 7 o'clock position and then start welding at 6.

Ok. No offense, I definitely appreciate any advice, but, how will moving the bottom tack over half an inch solve the whole pipe distortion/bowing problem, and help me slick a bead in there better?

[Poland308]

If your burning through the first tack and the pipe no longer has the suport on that spot to keep it from shrinking or moving.

[Poland308]

But when im done, the pipe is usually bowing and im not always to happy with how the root is looking especially my tie-ins to my tacks.

Plus it will help with your tie ins.

[Rick_H]

If I tack at 6 o'clock I start at 7 and weld through the tack.. Like Josh said this will help a lot, I also use less gap 3/32" in most cases, it shrinks up a little and I have no issues getting a nice flush root. You can butt weld sch 10 but the settings have to be spot on..... Do you feather your tacks with a grinder or just brush heavily? I run more amps, but I move pretty fast. Are you doing laywire or key hole and dab?

I always try to weld right through my tacks, if I need to stop I stop after I pass the intial tack then, feather if I can before re-starting, if I can't feather it (depends on WPS) I make sure I start about 3/8" from the end of the weld to ensure I have proper fusion.

Are these just small test pieces that are bowing or is this a long run you are having issues with as well?

[Otto Nobedder]

I do a fair bit of stainless pipe and tube, and I find my results improve if I intentionally fit the joint "wrong"... It seems the overall shrinkage is greater at the end of the weld, because of the effect of heat moving ahead of you, for want of a better explanation.

I'll fit a 5G joint, for example, with a 1/16" gap at the bottom, and a 3/32" or greater gap at the top, assuming I'm going to weld from 6 to 12. This seems to balance the uneven shrinkage.

It's more art than science, though, as the effect varies with wall thickness, starting temperature, and my ability to match my speed to my heat on that particular day...

My last 2" sch. 40 304 coupon for code refresher ended up about 1.5* off of straight. Fortunately, they were only looking at weld quality, not fit quality.

When the alignment is critical, there are fixes... You can dry-wash the long side of the joint to induce additional shrinkage on that side. Not "best practice", but sometimes "ya gotta do what ya gotta do".

Steve S

[Guido_fairtown]

If I tack at 6 o'clock I start at 7 and weld through the tack.. Like Josh said this will help a lot, I also use less gap 3/32" in most cases, it shrinks up a little and I have no issues getting a nice flush root. You can butt weld sch 10 but the settings have to be spot on..... Do you feather your tacks with a grinder or just brush heavily? I run more amps, but I move pretty fast. Are you doing laywire or key hole and dab?

I always try to weld right through my tacks, if I need to stop I stop after I pass the intial tack then, feather if I can before re-starting, if I can't feather it (depends on WPS) I make sure I start about 3/8" from the end of the weld to ensure I have proper fusion.

Are these just small test pieces that are bowing or is this a long run you are having issues with as well?

Yes i feather my tacks, and yes these are just small (4"-6" each piece) pieces for tests, 6g position. Also i was taught to backfeed the root, basically use a big gap, usually a 5/32 or 1/8, and then i feed the wire through the inside pipe, thereby putting in a root that has a little meat on it. When i do this its more of a keyhole method except i try not to let it keyhole, im continuously feeding wire into the puddle. Ive done some lay wire but i find when i do that sometimes my roots are a little concave/underflush and i also worry a bit about fusion, if the sides of the pipe were completely broken down or not. I want to make sure my welds shoot x-rays...
Are you using 3/32 wire?

[Guido_fairtown]

I do a fair bit of stainless pipe and tube, and I find my results improve if I intentionally fit the joint "wrong"... It seems the overall shrinkage is greater at the end of the weld, because of the effect of heat moving ahead of you, for want of a better explanation.

I'll fit a 5G joint, for example, with a 1/16" gap at the bottom, and a 3/32" or greater gap at the top, assuming I'm going to weld from 6 to 12. This seems to balance the uneven shrinkage.

It's more art than science, though, as the effect varies with wall thickness, starting temperature, and my ability to match my speed to my heat on that particular day...

My last 2" sch. 40 304 coupon for code refresher ended up about 1.5* off of straight. Fortunately, they were only looking at weld quality, not fit quality.

When the alignment is critical, there are fixes... You can dry-wash the long side of the joint to induce additional shrinkage on that side. Not "best practice", but sometimes "ya gotta do what ya gotta do".

Steve S

So i take it you are doing a laywire technique when putting in a root? Are you using 3/32 wire? What heat do you usually run at? Torch set up, gas lense, cup, etc.?

Ive been taught to backfeed my roots in but im willing to try laywire/pressure feeding...

[Otto Nobedder]

I free-hand anything under 6". Advance/keyhole/fill. I don't go lay-wire until the second pass, then it's still free-hand on small pipe.

On a 2" sch. 10, I'd guess I'm at 75-80 amps, on the remote for adjustment as I go. I do prefer 3/32 filler for my root pass.

Steve S

[Guido_fairtown]

I free-hand anything under 6". Advance/keyhole/fill. I don't go lay-wire until the second pass, then it's still free-hand on small pipe.

On a 2" sch. 10, I'd guess I'm at 75-80 amps, on the remote for adjustment as I go. I do prefer 3/32 filler for my root pass.

Steve S

Ok, yea i definitely free hand also. I never get to use a machine with a remote or foot pedal or anything, so im usually at around 50 amps.