Dave Lawrence
Marty Drinan and I recently tested some of the publishedknowledge concerning the ability to braze join stainless steel kegs toexterior fittings. Marty had acquired a 10 gallon cornelus keg andwished to convert it to a vessel with various side ports and pipe tapconnections. He had prepared the keg by drilling the correct size holesand had several 1/2" couplings that had been ground to fit theshape of the keg. I offered to try to braze the fittings on in returnfor some milling time on his grain mill. We finished the grain millingin jig time as Marty's mill has tremendous thruput, and the electricmotor takes all the work out of milling. We then cleared away the grainsupplies, and I got my oxy-MAPP torch out for the brazing.A review of several published articles in Zymurgy and severalwelding handbooks indicate that brazing and silver soldering ofstainless steel is a common industrial jointing technique. I havesilver soldered silver and copper for many years and have been experimentingwith bronze brazing of mild steel for about a year, so Ifelt sure that we could braze the fittings on the keg.
We used fender washers and thru-bolts to clamp the 1/2" couplingsto the side of the keg over the holes bored in the side. I fluxed thejoint with a combination of Handy-flux and borax. This combination hasworked well for steel and silver. Firing up the torch, I preheated the1/2" coupling before applying the torch flame to the stainless steel. Iwas able to get a bead of braze to flow around the first coupling andmoved onto the next. Within a few minutes, the stainless steel aroundthe first coupling began to crack as it cooled. The cracking occurredin the heat affected zone and extended into the unaffected portions of the wall. The cracks became quite large, extending as much as an 1-1/4" long and gaped up to a 1/8 of an inch wide. I tried fluxing with only one or the other of the fluxes I had and all subsequent joints cracked as well. I have to conclude that the extensive heating required to braze with a gastorch is not tolerated by the thin metal of the sides of a 10 gallon keg.
In retrospect, it seams that the large amount of metal side wallthat gets heated and expands, cannot subsequently return to the sameposition and thus fails by cracking. This is supported by the extensivebuckling of the keg side around the fitting as the metal cooled.
I recommend that anyone trying to attach side arms and otherports onto the side of a thin keg use mechanical fittings and gaskets oruse TIG welding techniques. The TIG should work as the amount of thinmetal that is heated is much smaller than using gas torch technique.Even so, I have a greater respect for welders who routinely join thinstainless and do such a neat job of it.
Finally, don't believe everything you read, at least about brazing stainless!
