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I've been working on repairing my front gate, which got hit by a car. It's also been a good opportunity to get better at welding (FCAW).

I'm having an issue doing some patch repair welds on the 2x2x3/32" vertical steel tube that holds the gate up. Unfortunately I don't have any pictures right now although I will try to take some the next time it happens.

The problem I'm having seems (to my untrained eye) to be caused by rust inclusions in the weld, which generally leaves me with welds that have small pinholes around the edges (which become apparent after grinding down the bead). That's my best theory.

The cause, I believe, is that the inside of the tube is severely rusted due to long term rainwater exposure. While I've fully cleaned the outside of the tube before welding, I can't clean inside the tube and I believe the rust on the inside is contaminating the deeper portions of my welds.

My question is: Is there anything I can do about this? Is there any way to achieve perfect welds when the opposite side of the metal is covered in inaccessible rust (and who knows what else)?

I've tried running over the holes with a lower voltage and feed speed just to fill them in with metal but when I grind those away, it just keeps moving the pinholes to the edges of my spot welds.

I hope this is clear. I'm actually OK, function-wise, with the current mediocre welds, since they're still sufficient and worst case I can throw some bondo over the holes or something. However, since this is welding practice for me I'd really like to get closer to perfect beads. Not quite sure what to do about this issue, assuming the rust is the issue (but like I said, that's my current theory -- I don't have any other ideas of what's going on).

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  • If you want to practice and develop skills do it on raw materials in controlled situations. Trying to get it perfect here without the underlying skills is an exercise in frustration.
    – whatsisname
    Commented Jan 23, 2021 at 6:46

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I am not an expert welder by any means but if you were to watch enough YouTube videos on the subject you would come to know that welding very thin materials is an art unto itself. You said nothing in your question about the type of welder that you use (ARC, MIG or TIG) but one of these types is probably going to be much better at avoiding melt through on thin materials.

From what I have learned it takes lots of practice to establish the expertise to be able to successfully weld thin materials. The 3/32" that you quote should be weldable without pin hole melt through with the proper skills.

I believe that if you can avoid getting the heat so high to avoid melt through that the rust on the inside should not be a problem.

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  • Thanks. I did mention FCAW, that's flux-core wire feed arc welding. Similar to mig but gas comes from flux inside the wire. :) Makes sense about the weld through and heat control. Although I'm not sure how to avoid contacting the other side when butt welding patch pieces into holes. Hmm.
    – Jason C
    Commented Jan 23, 2021 at 5:44
  • When butt welding patch pieces, make them tightly fit the hole and the just bevel the edges enough to get a good weld. That way you don’t go through to the other side.
    – Solar Mike
    Commented Jan 23, 2021 at 7:51

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