Welding exhaust pipe right off the manifold

Gary Fowler · Dec 17, 2015

The header pipes off the manifold on my RV broke off on one side due to an impact with road debris. I welded it back up using oxyacetylene torch and ER70S-2 wire but the welds really didn't like to fuse with the parent metal. Since it is right off the manifold, I suspect it is a chrome alloy of some type. It isn't stainless for sure but the mild steel electrode didn't want to fuse real weld and the inside of the pipe would "sugar" a bit after welding which tells me it must be 5%or more chrome content.
Anyone have any best guesses as to what kind of material the exhaust piping is made from.

Shield Arc · Dec 17, 2015

Gary I've read lots of times where people just braze that connection. I've never done it myself.
http://ganoksin.com/blog/cgmfindings/2012/10/03/metal-melting-points-guide-to-melting-metals/

yomax4 · Dec 17, 2015

Newer exhaust could be that new automotive 409 Stainless. It doesn't act like stainless at all. Not sure what you have but brass brazing could work. Not sure how it will take to the heat and vibe. Maybe a 3/32 or 1/16 stainless stick would be better.? You could look for some of that MG Easy Strike 1/16. or Mig it. If you have a close fit up, maybe silver solder with a little nickel in it like 50N. Strong and ductile.

George2615 · Dec 17, 2015

I had to make very short 90* bend exhaust pipe that came right off shorty headers on a street rod I had. On ready made 90's available in auto parts stores the sweep was too large and I didn't have frame clearance. Nobody makes a real short sweep 90* so I made my own. I cut the pipes to the size I needed and used oxyacetylene and coat hangers to braze together. Just had to get the pipe cherry red and flow the coat hanger in like solder. Worked very well.

tcartwri · Dec 17, 2015

yomax4 said:
Newer exhaust could be that new automotive 409 Stainless. It doesn't act like stainless at all. Not sure what you have but brass brazing could work. Not sure how it will take to the heat and vibe. Maybe a 3/32 or 1/16 stainless stick would be better.? You could look for some of that MG Easy Strike 1/16. or Mig it. If you have a close fit up, maybe silver solder with a little nickel in it like 50N. Strong and ductile.

Yup, usually 409. Has a dull finish and will show rust stains.

Gary Fowler · Dec 17, 2015

For sure could be a low grade of stainless since it only had a light coating of rust and dirt that I sanded off. It did require a lot of heat to fuse the ER70S-2 wire to it and did see a light oxidation (sugaring )inside after welding.
I have already completed the welding with the carbon steel rods so advice as to the right rod to use would just be informative for later use. I have welded SS with 7018 rods a lot of times with good results as far as fusion and strength (not breaking later) but never tried it with gas welding.
I guess now I will just have to wait and see how it goes with the weld. If it breaks again, I will have to have a muffler shop make this short portion and then weld it onto the original pipes which is what I started to do this time but decided to just weld it up and see what happens.

Gary Fowler · Dec 17, 2015

George2615 said:
I had to make very short 90* bend exhaust pipe that came right off shorty headers on a street rod I had. On ready made 90's available in auto parts stores the sweep was too large and I didn't have frame clearance. Nobody makes a real short sweep 90* so I made my own. I cut the pipes to the size I needed and used oxyacetylene and coat hangers to braze together. Just had to get the pipe cherry red and flow the coat hanger in like solder. Worked very well.

How well did the fabrication hold up?

muddstopper · Dec 17, 2015

My buddy that used to do exhaust always just used 70s wire in his mig. I never heard of any complains from anybody, so I guess it worked just fine.

George2615 · Dec 17, 2015

Gary Fowler said:
How well did the fabrication hold up?

I brazed up that exhaust system 7 years ago, sold the car 3 years ago, Saw current owner this past summer and exhaust is still fine. No leaks. I did paint the pipes with hi temp alum. paint when done.
I also used the same method on 409 stainless on an aftermarket exhaust system for a 396 Chevelle conv. I didn't want to use clamps for pipe to pipe connections so brazed them. Only used clamps for the pipe to muffler connections.