Multi-Pass Tig Welding Back Grind????

[StoneCold]

I could use some help on this. I have a problem with little tracks in the weld when I get to about the third pass on a tig weld. I have seen it on carbon steel and on 316L. At first I thought that I was getting the 316L too hot and that was causing it but yesterday I saw it on carbon steel. I have been very good about preparing the weld joint but I still get the tracks in the resulting weld.
I have tried to keep the tungsten clean. Should I be back grinding in between passes? Could that be the problem? It usually does not show up until I am on the third pass. What do you think?

Thanks
StoneCold

 

[metengr]

There should be no reason for you to back grind the GTAW weld passes.

Several questions;

The tracks that you mention, are these consistent in each weld layer that is deposited around the entire weld joint after the 3rd pass?

Is this auto or manual GTAW? What is the thickness of the weld joint?

Also, are you depositing separate welds on 316L ss and carbon steel or are you joining the two materials, as in a dissimilar metal weld joint?

 

[StoneCold]

metengr
Thanks for the responce.
It is manual GTAW.
The tracks are fairly concistant along the weld.
The tracks will show up in folowing layers if you keep depositing over them.
The 316L ss welds and the carbon steel welds are separate welds. I was just trying to explain that it happens on multiple projects and metals.
I will also tell you that I have never seen it happen to another guy who welds for us but he never does more than two passes of GTAW. He will fill/cap with MIG for CS or use a very narrow bevel and fill the stainless in two passes.
So it is probably something I do wrong but I don't know what it is.
The most recent example was on sch 40 4" cs pipe so the wall is about .375 inches thick. Butt weld, both sides beveled. Root gap about 1/16".
I was pushing the puddle and feeding the 1/16" rod in the front. The torch angle was tipped slighly back. Running about 175 Amps. 2%Thoriated tungsten 3/32" diameter. Hand ground to a point.
If I stop and regrind the tungsten and start again it does not go away.
Any suggestions?

 

[metengr]

After reviewing your post, it appears this could be a technique problem. It might be that as the joint angle increases you are not depositing the filler metal in a consistent manner or you are preferring to wash along the sidewalls not realizing that the joint angle increases in width resulting in a local low spot or depression that is being repeated.

Do you have access to any other experienced welders either inside or outside your company that could watch you and work with you directly to modify your technique. Once you modify your technique, you should be ok.

 

[StoneCold]

metengr
You are probably right, that it is a technique issue. I will see if I can get some help from a contractor that we use sometimes.
Thanks
StoneCold

 

[pipewelder1999]

Here are some questions that may help me. 175 amps and 4" sch 40 don't seem to mix to me. 1/16" wire is WAY too small for feeding adequate wire by hand in my opinion. It sound like you may be getting a "Centerline crease" that shows up when a concave weld bead is placed in root. If following passes remelt all the way to the root this will continue to show up. I may be all wrong. Here are some questions.

1) Are the tracks a single line through the centerline of the weld? If not what do they look like.

2) Do you have any pictures you could email .

3) Have you performed any liquid penetrant testing to see if this extends below the surface.

4) Are you walking the cup or freehanding.

5) What does the internal surface of the root look like and have you noticed it remelting when you deposit the following layers.

Well thats all I can think of.

Gerald

Gerald Austin
Iuka, Mississippi

http://www.weldinginspectionsvcs.com