oxygas welding of stainless

john02139December 2, 2009

I just bought a small (very small) gas welding outfit mainly to do repairs to a vintage travel trailer that I bought as a retirement project. My education is going well to the extent that in about a week I will be able to turn practice into useful work. For starters, I will be making a replacement for the rear 30" of the frame that is severely rusted. This will involve an assembly made of 1/8" mild steel angle and plate stock and should be no problem. It is my next project that I'm worried about. This will be the fabrication of fresh water and gray water tanks from 22 gauge stainless steel. Please tell me that I can get this done with what I've got and not have to get involved with electric welding and the whole new new learning curve and equipment expense that it will require. Any advice and/or sources of information on the subject of oxygas welding of stainless steel would be greatly appreciated.

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I hate to dampen your enthusiasm, BUT,,,,,.
While it is possible to gas weld stainless steel, it is not for the beginner. I never tried it with an ordinary torch, because the Henrob/Dillon oxy acetylene torch I bought 30 years ago was so much more controllable, I used it exclusively.

In order to gas weld stainless you must provide an oxygen free envelope to the area around the puddled material. This is very easily done with the MIG and TIG processes, by the argon shielding gas. In oxy acetylene you must first establish a neutral flame with the torch, and then add more acetylene, which will cause a secondary cone of flame to surround the brighter inner cone.
Within the secondary cone there will be an excess of acetylene, and a relative absence of oxygen. At the outer edge of the secondary cone, there will be oxygen present which is drawn into the flame from the surrounding air.

It will be difficult to get the two halves of the puddle to join up with each other because impurities on the surface of the puddles will have a high surface tension, and the puddles will be difficult to join.

You will have to use flux on the rod. It is available at welding supply hoses in a neat metal can with a small pop out disc in the center of the lid. This keeps the flux in the can from being overly compromised by exposure to ambient humidity. Prior to starting to puddle the work piece, heat several inches (not melting, just a little beyond too hot to touch) of the filler rod, and plunge it into the flux can through the small hole in the lid. When you withdraw it from the can, it will look like a sweater sleeve with a nice coating of flux.

Proceed to preheat the weld area by passing the torch flame over it for a minute or so. This can be done with a neutral flame to conserve acetylene. No harm will come of preheating with a neutral flame, only when the base metal is melted does the flame have to be fuel rich (technically referred to as a carburizing flame)

When the area is adequately preheated, open the fuel gas (acetylene) valve slightly, and return the torch to the starting point for your weld. Moving in a small circle, bring the metal to puddling temperature, taking care to avoid lifting the flame away from the work piece if it gets too hot. This will allow ambient oxygen to attack your puddled metal, and it will trash itself.

Heat control is by increasing motion, or piling in filler rod to help cool the puddled area.

Having said all this, I doubt that even with lots of experience with this process, I don't believe I'd tackle 22 gauge stainless with a torch. One downside of the gas welding process in stainless steel is that the advancement of the completed bead is so much slower than other more appropriate welding systems, warping is a big concern.

Oxy acetylene welding of stainless steel is also expensive in terms of consumed gasses, compared to the cost of argon for TIG welding, or tri mix or straight argon for MIG welding.

You might want to consider using 22 gauge galvanized steel for these tanks, and braze them using the torch. That would be much faster, and heat distortion would be very easy to control. If the seams are all on the outside the contact area between water and the brazed area will be quite low, and I doubt there would be enough exposure to have to worry about lead contamination.

If you should decide to use lead free solder on galvanized, then the acetylene torch is not your weapon of choice. A propane torch works better for soldering. Or you could go way back a couple of generations and find a blow torch and soldering iron to be your heat source for soldering. Just get it really clean before you start. Plenty of elbow grease with a tooth brush and acid, and then hit it with solid wire lead free solder.

If you do decide to braze or solder, the joints should be overlapped. Solder for sure and brazing to a lesser extent don't do well in butted weld joints.

    Bookmark   December 7, 2009 at 11:16PM
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