I was tig welding 16 guage 304 stainless tube today and when i fuse it together everything is fine but when I add 308L filler it looks dark gray and you can see it flow into to weld puddle when I add it. I used a scotch brite scuff pad to clean the filler rod and it does the same thing. WTF?

 

Sounds to me its poor gas coverage. Try different gas lens and cups. That or the inside of the pipe is not clean and when you use more heat to add the filler ur bringing it up into the puddle by penetrating the pipe. When you fuse a pipe or tube its not much heat so you will always get SOME color. I don't think a contaminant is the problem.
Hope this helps

 

this usually happens when you start adding filler as a beginning tig welder. I'm assuming you are dipping your filler? probable reason #1 is that it is actually poor gas coverage on the tip of your filler caused by retracting it to far when you pull it out of the puddle. The red hot tip of the filler will oxidize in the atmosphere and cause the problem you are having.

Possible reason #2 is that adding filler is slowing you down and you are heatsoaking the tube.

Its very likely a combination of both reason I just stated. Don't worry this happens to pretty much everyone the first time they pick of the filler rod.

I would ditch the dip method until you get the speed and heat correct. Just use a smaller filler (I like .035-.045) and just push it into the leading edge of the puddle. If it ***** up and runs away from the puddle just push it in harder. If it still ***** up lower your filler angle. It's very important that you push the puddle aggressively with the filler.

stainless tube is expensive. maybe work on some cheaper scrap to learn the technique then move to thinner stock. The principles are pretty much the same even when you are weldling 1/4 flat stock.

 

I have corrected the issue. It was poor gas coverage.