water + air + stainless steel = rust ? (2 pic)

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zzyvba

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Hi,

I cleaned my keg 3 weeks ago, and filled it with water to rinse. It was late and I was tired, so left the keg full of water and opened. However, I noticed there was rust inside the thread where the gas tube fit in the next two days.

here is a picture:


a closer one:




I read about the same issue here and thought my keg needed a passivation layer. so I cleaned it very well with green fiber scour pad and a stainless steel cleanser, rinsed and dried (it was clean and shiny) and exposed to air for two days.

Then, I filled it with water again to see if it was going to rust. and it did rust again.

the question is:

What am I doing wrong?


the water is tap water (hard and a little bit salty).

Does stainless steel rust even if it is passivated?

is hard water corrosive if it is exposed to air?
 
Bar keepers friend will help passivate that. If something non stainless like mild steel has rubbed on it, it will leave a rustable surface. You can get a ss brush and scrub it more, but only use that brush on ss, or it will also be contaminated.
 
You will get a bit of rust with stainless steel if you have it resting up against stainless steel and you leave it wet for a while. I've got stainless flatware, and a stainless sink, and I get little rust marks on my spoons when I leave them in the sink too long. It usually wipes away with a little rubbing and doesn't generally hurt anything.
 
Most stainless flatware isn't a very stainless stainless.

Less resistance or more resistance, it will still happen with enough time regardless. It's usually when high-chlorine tap water sits directly against the metal in close proximity to another separate piece of corrosion resistant or carbon steel that it happens the quickest.

Tap water usually has chlorine in it, sometimes lots of chlorine in it. When you leave it sitting on any form of steel, it will promote rust above and beyond what regular water will. The nice thing about stainless steel is that the chromium rather quickly forms a thin passive layer when exposed. That's why your stainless steel kegs can be scratched without starting to rust.

You probably shouldn't have to worry too much about continued rusting. Just take care to clean off the rust well.
 
Thank you guys,

well, if you ask anyone wants to buy a stainless steel why stainless steel? he would say because it doesn't rust.

I cleaned the keg for the last time and gave it a shot. it still rust like any other carbon steel would do, in just 24 hours.

Thank you again.
 
Pretty sure it actually takes a week or two to re-passivate. Unless there is some sort of carbon contaminant. plus, at the line between the liquid and air the effects happen more rapidly.
 
If there was any contact with carbon steel, it will rub off on the stainless and that will rust. Stainless threads will tend to gall (rub metal off the matching piece) so that's possible. I don't know what chloride attack on stainless steel looks like, but unless your water is super-chlorinated (like over-chlorinated and smells like swimming pool), I wouldn't worry about it.

And yes, BKF will scrub the rust off. I have a stainless sink that gets little rusty spots from baking pans.

If you are still concerned about your kegs, I recommend you send them to me for evaluation. It may take a few years--stainless rusts very slowly, you know.
 
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