A problem with "bubbles"....

[TxDarth]

Remember I am just a home hobbiest - bought my Miller 211 and Syncro200 for my hobbies.

Currently building an exhaust system for a project at home. I am using "U" bends to do the deed. I have some lap joints and some butt welds and one in particular is driving me crazy. I am using my 211 doing the rest in MIG - I started with TIG and then changed as I felt more comfortable there.

I am coming down to the finish line and I have on joint that is for lack of a better word "bubbling" and when I grid it down they show up badly. If I weld over it and then grind - more bubbles. I don't know what to do at this point other than cut it all out and make a new joint but I think I will have to remake this piece if I do that.

Open to suggestions on how to cure my problem.

[Keith_J]

Iron oxide of some sorts. I was welding a badly rusted diesel tank (yes, the tank had been flame cleaned and rust removed with phosphoric acid) and even the smallest pinhole would be impossible to fill without drilling each out to non-rusted sections.

If a bubble hole forms, let it cool, drill it out to solid material (diameter depending on thickness for full depth fusion) and then reweld.

Mind you, on my diesel tank repair, I had back-purged the tank (small 6 gallon generator tank) and STILL had your same bubble issues. Didn't matter if I used S2 or S6 filler.

[MMW]

Instead of trying to run a bead use a series of tack welds to seal it up. Pull the trigger to get a tack & then release. Let it cool just enough to solidify then do it again. Keep repeating this till it is welded. If you get porosity or bubbling then immediately stop & grind it out before proceding. Grind out the bad spots as much as you can before you start.

[TxDarth]

Thanx for the suggestions - will try tomorrow. I soured on it for tonight, watching football instead. I needed a break for sure.

[Coalsmoke]

When I was first learning tig I had a habit of running too hot. A little later I was building a hydraulic tank for a customer and had the same type of thing as you, porosity that wouldn't seem to go away. Took the problem to my mentor and he let me in on the fact that I was cooking the steel. Basically, moving too slow and too hot, which explained why the more I tried to fix it the worse it got. May or may not be your issue, but should be considered.

[Sberry]

Also happens when the wire feed is a pinch too slow,,, or can certainly add to the problem. On an exhaust joint they may not be that big of deal, lots of times they do not go all the way thru.

[TxDarth]

Problem is I see it and it would be on an area where it would be impossible to get at once installed. Then I know it is there also.

I will play to see if I can resolve.

[dondlhmn]

I have welded mandrel bent tubing for several exhaust projects and have found the same problem occasionally. It seems that the metal a lot of that stuff is made from is not exactly the purest stuff ever made and often contains strange impurites that give the same problem you are having. Is it possible that you have another chunk of that tubing or a scrap you can put in where you are now welding? Another thing to try to see what happens is to see if you have a scrap of any shape or size that was cut from the exact spot you are welding on now. If you can find such a piece, try welding on that and see if you get the same problem.....if so, I would bet a LARGE amount of my nickels that there is some kind of an impurity problem with that piece.