suck~back

sizzler · Thu Jan 23, 2014 10:16 pm

Hey guys ive got a question for ya.

Recently ive started pipe welding at my trade school. Running 6010 open root and 7018 fill and cap on 6" schedule 40.
I like to run things as hot as I can but when I do that on my root pass I encounter a lot of suck-back from the heat. (so im told by my instructor) so i have a few questions, is suck-back caused by running the pass to hot? Will it fail me on a test? and if so can I get rid of it just by reducing my amps?

Thu Jan 23, 2014 10:33 pm

That's a loaded question...

And you'll get responses.

Personally, I'd do that at 105A for a 1/8" 6010, but that's NOT a whip-n-pause technique....

Steve S

lazerbeam · Fri Jan 24, 2014 4:06 pm

Which method are you using to put your root in. If you are burying the rod then you need to put a little more pressure on the rod. If you are whipping then you need to see a keyhole. Which ever method you use, it is a combination of amps, root face and root opening. You will have to find out what works for you. With 6010 it is usually not suck back but lack of melt through that is causing the problem.

sizzler · Fri Jan 24, 2014 11:08 pm

I use a whip and pause motion. I set up with 1/8" land and an 1/8" root opening running anywhere from 50 to 60 amps.

Monty86LU551 · Sat Jan 25, 2014 1:29 am

sizzler wrote:I use a whip and pause motion. I set up with 1/8" land and an 1/8" root opening running anywhere from 50 to 60 amps.

with that method you should probably run a little hotter. I usually run around 75-80. Which is still cold for some. Its all about what your comfortable running. Keep a key whole but don't let it blow out. And keep a tight arc.

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wheresmejumper · Mon Jan 27, 2014 4:26 pm

It seems you heard your instructor wrong.suck back doesnt happen on the root pass, it happens TO the root from too much amps or too little travel speed on the hot pass.

Monty86LU551 · Mon Jan 27, 2014 6:20 pm

wheresmejumper wrote:It seems you heard your instructor wrong.suck back doesnt happen on the root pass, it happens TO the root from too much amps or too little travel speed on the hot pass.

Running a root to hot will not cause suck back. What will cause the "appearance" of suck back is not enough heat i.e. no penetration, to much land and not burning through it. If you burn hot enough of your hot pass you will push your root in better. That's why flush root is good because by the time your capped and finished you should have pushed in your root no more than an 1/8 inch.

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Monty86LU551 · Mon Jan 27, 2014 6:25 pm

Also if when you tie in to a tack and you don't weld past your tack then you can get a spot that doesn't tie in all the way. Make sure you feather your tacks good and weld at least half way up on your tack to make sure your tied in and it doesn't suck back on you. Keep it pushed in

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Vince51 · Fri Jan 31, 2014 2:23 am

Combination of things cause suckback. I'll list some and you'll have to experiment to fit you.
1. To many amps combined with travel speed being to slow. Makes a wide flat or sucked back root on the bottom of the pipe.
2. Bevel peeled back to far with a wide gap. The bevel gets hot and sags because there is nothing cool to support it.
3. Long arc length. If the arc is not shoved inside the pipe metal will fall out of the keyhole.

These things will happen on overhead plate welds also

When coming from the bottom I watch the flux on the rod. If the arc is tight enough you'll see a point form at the end of the rod.
Oscillate the rod side to side and you can watch the point wonder side to side. When you get around dead mans corner a circular motion inside the keyhole will help you break the landings down evenly. Personal preference, but 70-80 amps works for me, but i can run up to 100 or so. Keep that fire inside the pipe and good luck.

Vince

Vince51 · Fri Jan 31, 2014 2:27 am

Forgot to tell you. In general if its sucked back below base metal it will be rejected. There are ways to get around suckback on a field weld xray, but if the root is visible to an inspector suckback is a defect( failure).

Vince

Mongol · Sun Feb 02, 2014 4:14 pm

Vince51 wrote:Forgot to tell you. In general if its sucked back below base metal it will be rejected. There are ways to get around suckback on a field weld xray, but if the root is visible to an inspector suckback is a defect( failure).

Vince

Not necessarily. AWS D1.1

4.9 Method of Testing and Acceptance Criteria for WPS Qualification

4.9.1.1 Visual Inspection of Grove Welds

(6) For CJP grooves welded from one side without backing, root concavity or melt through shall conform to the following:

(a) The maximum root concavity shall be 1/16 in [2 mm], provided the total weld thickness is equal to or greater than that of the base metal.

(b) The maximum melt through shall be 1/8 in [3 mm] except for tubular T-, Y-, and K- connections, where melt through is not limited.

Vince51 · Mon Feb 03, 2014 1:17 am

Agreed not always, but in general. Not every weld is subject to asme section 9 criteria. I think its a good idea to familiarize yourself with different code books. If anything to understand QC lingo.

Arizona SA200 · Wed Feb 05, 2014 8:14 pm

A consistent land and gap is key to good fit up. Bevel angle isn't as critical. My theory is nickles down dimes up, meaning nickle land and gap for downhand and a dime for uphand. Rod angle can can change thing too, trailing angle will seem colder(less penetration) and leading angle will seem hotter(more penetration). Keep the land and gap the same until you find the "sweet spot" then its a good idea to practice with different lands and gaps as in the field nothing will be consistent.

sizzler · Sun Feb 23, 2014 7:23 pm

Thanks for all the replies. Ive been messing with it every day pretty much so far I've found to like a 3/32 land and a 3/32 root opening running 60 to 70 amps with seems to work for me in 6g but not that we'll in 5g, it's probably just lack of experience and practice but do you guys change anything going from those positions to the next? A another question as long as you don't have any holes or anything is it possible for such back to show up in an xray?

Arizona SA200 · Mon Feb 24, 2014 7:53 pm

As far as suck back on Xray its hard to say. Xray is a density scan so if you have 1/32 suck back on the bead but your cap is 1/16 proud of the parent metal then chances are it wont be noticed. They will pick up on discontinuities in the root, porosity and wagon tracks. The Xray looks for "less dense spots" vs the parent metal if that makes sense.