Brazing

I'm looking into brazing couplings to kegs because of the cost of Tig welding. For a one hour minimum of $65.00 at the welders it's not cost effective to have one coupling welded. I can p/u a brazing kit a the Home depot for that price. Dose anyone have any experiance with this?

It can be done but brazing stainless is challenging. Stainless doesn't dissipate heat well so you have to be really careful about not over heating the thin metal of the pot/keg. If you have experience brazing or know someone that can help it shouldn't be a problem though.

I don't think homedepot will have what you need, you really need something like an oxy-acetylene setup to braze, propane isn't enough.

It it technically possible to soft solder stainless with propane and the right flux but the flux is nasty stuff and its very challenging to do, the joint will also be weaker and less heat resistant.

I believe that Home Depot does have a brazing kit that you can buy, comes with oxygen and acetylene.

I have found that using silver solder works just fine for fittings though, like previously stated the flux is some strong stuff but as long as you take your time and only apply it where necessary the outcome is wonderful. I've silver soldered multiple valves and couplings to my keggle and have never had a problem with a leaky or weak joint. I highly recommend using silver solder, only costs about $8.00 and you get enough to take care of at least 3-4 joints.

Go to a welding supply and get a silver solder kit with a liquid flux suitable for stainless. A melting point of 430F was easy to work with and is cool enough to avoid overheating. Make sure your tolerance is tight so you don't to try filling gaps.

Found some stuff called Stay-Brite looks like it may be the way to go.

Like already mentioned, stay away from trying to braze. Silver solder with the Stay -Brite flux appears to be the way to go. There is a guy on the B3 forum that posted several picts a while back and the results are great.

You will want to pick a fitting with some surface area though and not a regular coupler. The secret to getting any strength out of the joint is to have some surface contact between the fittings and not just edge contact. Try to find an adapter that has a shoulder on it.

I just checked out that thread. good stuff there. my only worry is when I crank on the valve will it hold? or should I assemble everythin and then solder

Just remember that where ever flux is, your silver solder will flow there. You can move the solder around by moving the torch to areas that need more coverage, the solder should flow to the heat, if not, add more solder. A fitting with a flange or some surface area to silver solder to will work better. The joint will be much cleaner and stronger with a tight fit. Harris Stay-Silv works well too...paste form flux.

If you can have the couplings OD machined down, an example of a 0.060" deep step plus a little longer than the thickness of the kegs side wall allowing for the keg's radius so the coupling sticks thru the keg at the sides and not just the top and bottom inside the keg. For this I would machine back 0.125" for this step as the coupling is plenty long, even a half coupling would work for this as my first choice. Yes you can soft solder stainless steel as easy as copper with a propane torch provided you have a big enough torch for heating. Use a stainless steel flux or cut muratic acid cut 50/50 with water also works great. Do Not Over Heat! Acid brush on the flux then solder away as if it is copper, actually it solders better than copper pulling in the solder when the joint is ready and hot enough. Drill the keg out first then machine the coupling for a snug fit vs making the kegs hole match the couplings step. This step will greatly increase the joints strength with the added step surface area especially with a snug fit to begin with. With a grinder then a flap wheel grind down and polish any coupling sticking thru to a flush finish inside. I will do this step process but Tig the outside then Tig fuse across the tight hairline crack joint inside the keg to keep any and all nasties from the joint. I would rather use half couplings on every fitting including those that will have a compression fitting on the inside for a compression siphon tube. With that coupling the end of the coupling sticking thru will be kept flat for the NPT adapter to 1/2" compression fitting to bottom out against the coupling as it might not tighten up before bottoming out. This would not be good if the coupling was radiused to the kegs inside. For the sight gauge and temp probes I drill out the threads on the inside to prevent crap from collecting in the threads, you only need 0.500" of threads on the outside of the couplings for your fittings and valves to attach to as they will become tight on the NPT before bottoming out against the coupling. JMO's here.

Actually, how about feeding the compression end of the fitting through a hole in the keg until the center hex bottoms out and soldering there. You can then thread the ball valve right on and you put the compression ferrule and nut back on for the siphon tube?

I know that board member/expert kladue has done this. I had asked him about it just a short whil back. Listed below are the instructions he gave to me.

Yes you can silver solder with 56% silver solder and the stay silv flux, the propane burning "turbo torches will produce enough heat to get the job done. Solder used was Harris safety Silv 56, flux was Harris Stay Silv white flux. Supplies will cost around $30 for small container of solder and ~ $4-$5 for flux which will last quite a while. you can thin flux with water to make a thin slurry to coat area to be heated, should leave a white layer on metal. Spend a little time in joint fit up to try and make joint gap as small as practical for stronger joints with less solder. The solder and flux are available at the Airgas facility on McGilchrest street by the airport, an equal product by other supplier will work the same, just make sure solder is cadmium free.


Step 1: clean area where solder joint will be with scotch brite.
Step 2: Coat area where solder joint is on both sides of keg and fitting, make area coated at least 1" wider than joint area to limit heat effects on surrounding metal.
Step 3: Apply heat by fanning flame across joint area slowly to prevent overheating, flux will change from white to transparent as temperature rises, watch metal color and try not to go lighter than dark red.
Step 4: Apply end of solder to joint and fan flame across end of solder and solder should turn liquid and flow into joint, solder will also flow towards heat and could flow away from target area if you are not carefull. If metal turns black from too much heat, cool metal down and sandpaper bright again and start over from step 2.
Step 5: After joint is left to cool naturally, use hot water and stiff brush to remove flux residue fom both sides of solder joint.

Bobby_M said:

Actually, how about feeding the compression end of the fitting through a hole in the keg until the center hex bottoms out and soldering there. You can then thread the ball valve right on and you put the compression ferrule and nut back on for the siphon tube?

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That's ok Bobby if you plan to keep yourself limited with a soldered compression fitting to the keg. With a coupling soldered to the keg the ability to unscrew and add a different fitting is a option still available should one do a design change or apply a different idea. I stated a coupling for a reason. Soldering is on the bottom of the list, well one step up from weldless, brazing one step up from soldering. I like Tig welded couplings nothing beats the strength of stainless plus my favorite for quick easy fitting changes should I wish to do so.