Rust in Keg

[Carltortoise]

Hello. I have a SS Keg that I was planning on using to distill some vodka tomorrow. I looked inside of it and noticed some rust around the fitting where the heating element goes in. Is this keg still safe to use with a little rust inside of it? What are the dangers? Will the rust end up poisoning my vodka?

[shadylane]

rust poisoning my vodka?
No, a little bit of iron oxide isn't poisonous.
Professional welders can make rust proof welds on stainless steel.
The quality of my welds aren't that good.
I'm not proud of my welds, but they are safe.
With a little bit of additional info, one of the better welders here may be able to explain how to stop the rust.

[srs787]

I would put the distilling tomorrow on hold for a while. A few questions. Has this still been tested with a water run, a vinegar run, and a sac. alcohol run. Do not run the still unless these have been done. I would check with the builder of the keg, asking them about methods and materials used. A little rust might not hurt you. But there should not be any rust in the keg. Stay on the safe side.

[Carltortoise]

I've done a water run, vinegar, and a couple cleaning runs. Then I've distilled spirits 3 or 4 times. My setup is a keg with a 1" hole drilled through it and a SS nut welded over the hole. The heating element screws into the nut. It looks like there is just a little surface rust on the nut. I doubt I could get a picture, but I'll try. I must have bought a cheap nut or the welder messed something up. I'm not afraid of it leaking or anything like that. Structurally speaking its ok. I just didn't know if there were any health risks associated with having some rust in my wash when distilling.

[rad14701]

Sounds like you either didn't get a SS nut or your welder didn't use proper welding rod or technique... Your spirits should be safe to drink regardless...

[Carltortoise]

OK, I'll use it a couple more times and then scrap it when it gets really bad. Maybe I could sand it a little to make it last longer. I'm pretty sure it was a good nut. I got it from a plumbing supply place and it cost like $8. I should take it to the welder and make him buy it from me. Even if it was the nut, the welder should have been able to recognize that I had a bad nut and told me it would rust.

Thanks for the help

[DAD300]

Even with SS to SS with the proper filler (or no filler) it will rust if the weld isn't done right (shielded on both sides) or treated right (passification) after finished.

I recently cut open a keg I had TIG welded a 304 ferrule to. There was rust on the inside of the weld. I didn't shield the inside properly.

[Schroeder]

This quote is from an appendix on brewing metalurgy written by John Palmer. The parentheses are added by me.

"...high brazing (/welding) temperatures can be bad for stainless steel. At those temperatures, carbon in the stainless steel can form chromium carbides which takes the chromium out of solution, making the steel non-stainless near the joint. This area is prone to rust and cracking after it is in service. The problem cannot be fixed by re-passivation so it is best to avoid excessively heating the parts during the braze (/weld) and keep the total time at temperature to four minutes or less."

The reason that TIG is more effective than MIG or brazing for joining stainless is because it results in the lowest overall weld temperature with the smallest weld-pool (cools more quickly), and therefore the lowest chromium carbide development.
I have MIG welded 304 stainless with 303 wire and tri-mix gas and still had problems with small rust spots after thoroughly cleaning, and pickling after the weld was complete.
I have also used 45% silver solder to join 2 pieces of 304 stainless steel, and done a nitric acid pickle and polish and had no signs of rust develop. (make sure to clean the area thoroughly first and use enough flux, and one specifically for stainless.
Elsewhere in the article (or possibly only in the book) Palmer also suggests that silver solder can be effective for joining stainless parts, provided you can heat the area quickly to temp for the brazing, but not exceed the temperature that the carbides develop at.

Lots of other usefull information in the article as well
url for full article...
http://www.howtobrew.com/appendices/appendixB.html" onclick="window.open(this.href);return false;" rel="nofollow

[bellybuster]

contrary to popular belief even SS can oxidize/rust. I would guess that a good percentage of folks that have welded in stuff on their kegs have rust. Most never look..... (possible solution?)

[Schroeder]

[quote="Schroeder"]
"... The problem cannot be fixed by re-passivation"

Also, avoid any chlorine based cleaners and sanitizers. Stainless steel is "stainless" because of protective nickel and chromium oxides that form on the surface. Chlorine is highly reactive and will strip off these oxides leaving the Fe exposed and cause rust. I have seen hypochlorite sanitizers eat holes right through stainless steel at work.

The only way to avoid it is to do it right the first time. You cant fix it.