Soldering stainless steel couplings

[cjang]

I thought I should contribute to HBT in return for some great advise. Here's a more detailed description of my attempts to solder a stainless 1/2" coupling as part of a hopback. It's a practice run before I do it on a precious keg. It turned out really well and was super simple once I got it all together. My first run was a little sloppy but I figured it out on my second one.

Here's my first attempt. The solder was a bit sloppy I was not level and the solder pool ran so I did not have enough solder and I did not heat evenly enough.

Step 1: Assemble your flare tool (This was inspired by the soldering stainless steel thread. They call it a keg tool)

grind your mandrel out of a 1/2"x3/8" coupling. (Grind the 3/8" side) I used a bench grinder but I think holding the coupling on a vise and using an angle grinder should give fair results.

Parts:
1/2" x 4" full thread machine bolt
1" x 1/2" coupling or 1"x1" coupling
1/2" nut
various washers

Step 2: Drill your hole (make sure it's just barely large enough to fit your mandrel)

Step 3: Assemble flare tool.

Step 4: drive mandrel into wall.

Step 5: Disassemble tool.

Step 6: remove mandrel with hammer (rubber or deadblow so you don't ruin anythink)

Step 7: Clean coupling and hole. Fit coupling into hole.

Step 8: Drive coupling into position (I want it flush with the interior.)

Step 9: Place onto a stable surface with the coupling pointed down and PLUMB. This is critical so the flux and solder pools stay in place.

Step 10: Apply flux. (You MUST use flux designed for stainless.)

I use stay clean. I got it from an air gas dealership.

Step 11: Bend a ring of solder using the coupling as a form and lay it on top
of the flux.

Step 12: Solder. Heat the coupling from the outside using a propane torch. Don't heat the thin metal. Heat until the solder flows and forms a nice pool around the entire coupling.

Step 13: Allow to air cool. Don't quench with water since this may weaken the joint.

Step 14: Clean! You must clean off the flux since it is a strong acid and will cause corrosion wherever it sits. Rinse with water and scrub off all the slag.

Hope this was useful. I plan on doing the same to my keg when I have time. I like this alternative to welding since it's so accessible to most average homebrewers. The equipment is cheap. The tool was ~$10 to build. You don't have to be particularly skilled to get things nice and smooth.

Charles

 

[diodeart]

thank you. just what a non-welder needed. subscribed.

 

[Geordan]

Great guide, very helpful! Have you done any "stress testing" on the joints? Do they feel reasonably strong when compared to welded couplings?

 

[psbuckland]

I've used the same technique on all my kettles. The joint is very strong. I've never come close to dislodging it while torquing down on the couplers.

 

[cjang]

No stress test per se but I'm confident that it's stronger any damage you can do with basic hand tools. Honestly, your kettle walls are likely weaker than a properly soldered joint.

 

[naga77777]

ANything specific you should use to clean the flux off?

 

[jsguitar]

ANything specific you should use to clean the flux off?

Barkeeper's friend works great for cleaning the whole area up.

 

[Daddo07]

Do you plan on grinding the joint down to smooth and flush it so it is "sanitary"? I'm not making a suggestion, really asking if that is the thing to do or not. Unfortunately I've already gone threaded on all my bulkheads or I think I'd do this.

 

[cjang]

I neutralize the flux with a baking soda & water solution (I keep a squeeze bottle filled with a baking soda solution whenever I work with this flux just to be safe.) Then just scrub with a brass or stainless steel brush. If there's still discoloration, then I turn to barkeeper's friend or oxyclean.

I'm not planning on grinding it down. I would not consider these as clean as sanitary welds. If I were to do this on a fermenter, I'd keep the solder on the outside since the flare is pretty smooth.

 

[naga77777]

TOtal noob question here, but just wanna make sure.

THis stuff is safe to be in contact with boiling wort for an hour, right? Like food-safe? I'm assuming so, since my copper plumbing pipes are soldered, but they aren't getting boiled.

reason I ask, is I bought a stainless mash paddle that has a small hole in it, and i want to plug it with solder. But i leave the paddle in the boil to keep it sanitized so i can stir while chilling with an immersion chiller.

 

[cjang]

Depending on what solder you use, it should be totally safe. Get lead free plumbing safe solder. No flux or acid core, no lead (Pb) or antimony (Sb), nothing for electronics. If you're super concerned, look at the alloy. Some combination of silver (Ag), tin (Sn), bismuth (Bi), copper (Cu), or zinc (Zn) should be safe. I use the Oatey safe-flo from home depot.