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TIG Root suck back...

by Radu P. Laurentiu
(Wheaton, Illinois)

Today in class I made my root of 3/32" on a 6" carbon steel pipe coupon. I don't have a long piece of pipe, nor do I have the luxury of purging my pipe with Argon, because it's a college, and they don't allow us to just run Argon into the pipe freely like we would like... probably too much liability on the school.

Question 1: Am I going to be able to do a decent root pass without the suck back on the root, if I don't purge it??

I was having a hard time getting a key hole because with the 3/32" root gap, after I tacked the pipe coupon in 4 places, I realized that the root gap tightened in even more, and it wasn't even 3/32" any more. Because of it my root gap was real tight, and when I turned up my amperage to make a key hole, I was melting the top part to the bottom without even applying any filler rod.

Question 2: My question that I asked earlier, when I correct the root gap to 1/8" and even without purging it with Argon would I be able to do it without a suck back??


Radu P. Laurentiu



yes it is possible to get a decent root without argon on carbon steel. If fact, that is the way it is done all the time in pipe construction industry...

strive for a 1/8" gap and after tacking the gap should be just tight enough that a 1/8" rod will not slip thru.

there are 2 main methods for welding the root pass....

keyholing and lay wire.

with keyholing you usually use the 1/8 gap with 3/32 wire and just enough amps to keyhole and you dip the rod in and out of the puddle as you move the tip of the tungsten from wall to wall tying them together...just enough amps so that you see the corner of the bevel barely keyholing.

the other method is to use a 1/8 wire and rest it in the gap and just bare down on it with the tungsten using just enough heat to see the silicon ball swimming.

either method works once you perfect it.

things to watch are:

careful not to use too much side to side movement with the electrode...(causes suckback)

watch the torch angle too...keep it as straight in as possible with only about a 5 degree push angle

thanks for the post,


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