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My electric kettle (Brewista BKV12S02-CEV, if you're interested) fell on its nose (?), and now leaks water (one drop at a time) at the point where the swan neck touches the body of the kettle. The kettle is made of stainless steel.

enter image description here

Food-safety is very important, so I tried soldering with S-Sn97Cu3 with the predictable result that the solder didn't adhere to the stainless steel properly and just rolled off. Is soldering this a good idea? If yes, what solder, flux, etc. should be used? Or is soldering a bad idea?

The repairs must be food-safe, i.e. no toxic flux, etc.

Update: I used S-Sn97Cu3 with a water-soluble flux (Cu-Roflux 39, if you're interested) and a butane-driven soldering lamp (a normal soldering iron was apparently not hot enough. The result looks like this and (almost) doesn't leak anymore:

enter image description here

It's not a pretty as it used to be, but it works. The solder and flux are used in Germany to solder copper pipes for drinking water, so this should be fine.

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I would use caution on solder, as many solders have lead in them. For as to why solder is not sticking, y guess is you are not getting it hot enough.

I use a silver solder (actually it’s only ~15% silver), but lead free, for doing jobs like this and a oxygen acetylene torch. Propane and mapp gas are not hot enough for silver solder. There are some lead free solders that may work with mapp gas.

You have to get the metal really hot, and it may slightly discolor, but I have sealed stainless several times using a small oxygen acetylene torch.

Don’t forget to use flux (I use stay-silv) with either method.

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  • If you don't have an oxy-acetylene rig handy, ask around welding shops for someone that can do this kind of fix. 20 bucks and a six-pack usually gets the job done. May 8 at 14:46
  • Chances are fair to middling that you'll get the scorch marks off afterward with a scotchbrite pad. Otherwise, you have a one-of-a-kind kettle. May 8 at 14:47
  • The original construction was very likely silver solder . May 8 at 15:15
  • Is there any hope that this kettle's plastic parts will survive an oxy-acetylene welding operation?
    – jay613
    May 9 at 0:40
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    15% silver solder can be done with propane, but works better with MAPP or Acetylene. acetylene is needed for silver-free brazing.
    – Jasen
    May 9 at 11:24
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Soldering stainless steel is tricky, because the reason that stainless steel is "stainless" is a protective oxide layer.

Using flux designed for copper may not work well, or at all, becasue copper oxides are more easily removed.

While the joint needs to be "hot enough" to work, "too hot" is very possible and generally requires starting over from scratch, since it burns off the flux.

For soldering (on anything) to succeed, you need the joint to be mechanically clean (scrubbed, sanded, wirebrushed) to remove dirt and major corrosion. It needs to be chemically clean (removal of thin oxide layers with flux) and it needs to be at the right temperature (the metal of the joint should melt the solder, you should not be melting solder with your flame directly.)

At the correct temperature and with a properly clean joint, the solder should wick into the joint by capillary action. That will not happen at ANY temperature if the joint is not clean.

The above holds true both for "soft solders" (true solder, below 800F) and for "hard solder" (technically a brazing process) also known as "silver solder" - which was less confusing before there was low-temperature solder with silver in it, as lead-free solders became the norm. The fluxes and temperatures differ. The common lead free solder of the food industry was 95-5 tin-antimony before those other solders came along.

If not using stainless-steel-specific flux, you can sometimes succeed by wire-brushing with a liquid or paste flux on the joint, as the flux will prevent or reduce immediate attack by the oxygen in air after the bristles scrape it away, and then you can heat and solder immediately. Better success is had with stainless steel specific flux. Any flux residue should be removed by through cleaning afterwards (stainless is common in food-service equipment, so solders, fluxes and cleaning processes suitable for items in contact with food are plentiful in the marketplace.)

Alternatively, the item could be Tungsten Inert Gas welded, by a skilled operator (not a job you want to try for your first one - it's tricky welding thin stuff) - again, common in foodservice. Restoring the color and passivating (removing free iron, typically with citric acid) the surface in the "Heat Affected Zone" are normal post-welding processes.

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  • This is a very good crash course for soldering. I wish I had found something like this earlier. Thank you!
    – mkl
    Aug 3 at 15:35
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Jb weld or epoxy. You need to patch the hole, not necessarily weld it

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