Adventures in Hot Metal – Part 1

I did my first metal torch work yesterday, with mostly successful results. I used Muggy Weld SSF-6 High Temperature Silver Solder to close a hole in a damaged exhaust pipe using Lee’s oxyacetylene torch.

I have an exhaust pipe on the van that was leaking when I bought it. I got a $175 replacement from Mercedes, and now, less than two years later, it’s leaking in the same fucking place again. The pipe is solid stainless steel, and is only warrantied for 12 months, but my dealer said he’s still willing to send it in for a repair.

Luckily I kept the old pipe. Hoarding for the win!

There was a triangular tab that had been ripped open, and the flange seam was also coming apart, as you can see here:


Welding the stainless steel correctly would require a high-end TIG setup with the ability to backfill the inside of the pipe with argon, which we don’t have out here. I also have no welding experience, an it would require a skilled welder to pull off. However, Muggy Weld makes this high temperature silver solder that will work on stainless steel and melts at 1150 o F. It’s very expensive at around $30 per stick, but if it solves my problem, it’s worth it.

Lee got me checked out on his oxyacetylene setup. We welded some mild steel together to get a feel for the tools. Welding is very intense and alchemical, and I liked it right away!


Practice weld on mild steel

First I cleaned off the work area with a wire brush to get it as clean as possible. It’s important to remove as many impurities as possible to get a clean bond.


First I had to drill some very small holes to secure the wire ends:


Easier to see the hole with something white behind.

I then wrapped the target area with the wire as tightly as possible to make a good adhesion surface. If I can get the entire thing bonded, it should be *much* stronger than the original pipe:


I then pulled it tight from inside the pipe:


I originally tried a rosebud tip, which is for heating larger areas, but it was so big I found it very hard to control. I went back to the welding tip, which is much narrower. With brazing, one wants to heat the work surface enough that the solder will melt without the flame being present. In this case that was very hard, because there were three radically different thicknesses of metal. The flange is pretty thick, the pipe is pretty thin, and the wire is *very* thin.

I overheated the metal because I didn’t have good enough lighting and couldn’t see the solder melting correctly. What I did see were beads of solder forming and falling off, a sure sign that the piece isn’t hot enough. However, the solder *was* flowing into the gaps, I just didn’t see it. While trying to heat the metal enough to get the solder to flow, I ended up blowing a much bigger hole than the one I was trying to repair into the pipe!


A friend with a bit more experience came by about that time and helped get me back on track. Luckily the repair method I used for the first hole also works for the second, and I had a better feel for the setup now. I added a bunch more coil, then brazed all that as well.

The final result is ugly as fuck, but test it with my mouth, it feels sealed. I’d like to pressure test it with my compressor before installing it, though. I went back afterward, using what I had learned, and re-heated the thicker puddles of solder to get them to flow back into the piece.


One of the two brackets that hold the middle of the pipe was also broken, so I made a new one out of a stainless steel hose clamp. These are important to reduce load on the ends of the pipe, which gets very hot when operating.



Overall I’m happy with how it went, largely because I knew how incompetent I was and that I would make mistakes. Assuming it still fits on the van and actually works, it’s successful.

Next is pressure testing!

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