Bleach on Stainless Steel. What happens?

neilho · Apr 22, 2021

I have some 304SS aerators that get clogged with bacteria occasionally and have been dousing them in bleach. Works great to kill bacteria and clear the pores, but also produces something that looks like rust.

The intertubes says it's a nono, but as usual doesn't say why. Anyone here have experience with this?

BT Fabrication · Apr 22, 2021

it is an oxidiser with an acid salt. Acid eats the passivated layer allowing the salt to react to the iron and causing it to rust.

chemical name is sodium hypochlorite. also not 100% sure but probably something to do with the negatively charged ions of oxygen.

Mike C. · Apr 22, 2021

Problem is it's 304. If it's 316, that won't happen. 304 is kinda, sorta stainless.

BT Fabrication · Apr 22, 2021

it will still happen with 316 also. acid will still eat the passivization layer, that is why harsh acids only go in teflon or glass tanks.

Asquith · Apr 22, 2021

Corrosion pitting and stress corrosion cracking.

crossthread · Apr 22, 2021

I don't understand how the acid will eat the passivization layer. You passivate stainless with nitric acid.

Mark Rand · Apr 22, 2021

Specifically, the chloride ions stop the passivation layer from reforming. That's what I was told many years ago by one of our metallurgists, anyway.

Scottl · Apr 22, 2021

get one of those biocides meant for humidifiers.

Bill D · Apr 22, 2021

would lye do the same thing in reverse?

cudafamily · Apr 23, 2021

There is no acid present. Bleach is a basic solution. The Chloride ions are very destructive to all stainless materials forming metal chlorides as they react.

boslab · Apr 23, 2021

This is sort of interesting, it was an experiment I did whilst studying metallurgy a long time ago, 2 beakers salt water, 2 bits of stainless steel plate, about 1/8”, an elastic aka rubber band was put round one plate, pretty tight, the other without, the plates were dumped in the beakers and left.
They were checked weekly, the elastic band proceeded to cut its way through the plate, at quite a fair speed, I think the message stuck, disrupting the oxide film causes crevice corrosion, beware!
The hypo stripped the oxide result, corrosion, there is iron in stainless
Mark

BT Fabrication · Apr 23, 2021

passivization eats the top layer of material away, low enough solution that it does take of a few um of material to clean the surface, then washed away within hours it rebuilds the chromium oxide layer protecting the iron underneath.

that's why you need to neutralize the solution applied of hydro flouric acid and nitric acid mix or it will continue to corrode afterwards.

BT Fabrication · Apr 23, 2021

also just found this article about it.

https://www.texwipe.com/Content/Images/uploaded/documents/Technical-Data/Stainless_Steel_Bleach.pdf

Part of the article,

The sodium hypochlorite found in bleach and NaDCC is the active antimicrobial ingredient belonging to the oxidizing group of disinfectants. They form hypochlorous acid (HOCl) in water which interacts with biomolecules found in microbes resulting in cell death.1 – 7

neilho · Apr 23, 2021

Great article, thanks for the post. Suggests NaDCC, a chlorine based non corrosive alternative to bleach, too.

Also discovered that boiling the aerators in water is a good way to kill bacteria, too. Doh!

Pete Deal · Apr 23, 2021

I used to work in pharmaceutical manufacturing. We had some problems with stainless rusting (304 and 316) when processing certain formulations. It was determined to be chlorine. For good chlorine resistance we had some of the equipment made of hastelloy and problem solved.

BT Fabrication · Apr 23, 2021

i would be guessing, these aerators are used in the beer industry?

Big B · Apr 23, 2021

I'm no expert on stainless but from what I've read you can buy stainless that is corrosion resistant, wear resistant, and a lot of other qualities. I think if you look you can find the right kind that won't have that problem.

TDegenhart · Apr 23, 2021

This something salt water boat owners know. Stainless does not work well in salt water because of the free cloride ions. Use navel bronze or similar instead. Think propellers on ocean going ships.

Tom

mixdenny · Apr 23, 2021

From direct experience we had entire SS strainers in a tank eaten and nearly gone after filling the tank with bleach and setting for a week. These were probably 1/8" thick drilled plates. Another time we dropped hex nuts into bleached filled SS catch pans as we took hydrazine lines apart. Over night (or maybe a weekend) some of the nuts sunk through the pans making hex shaped holes.

ezduzit · Apr 23, 2021

Monel is often used in place of stainless for its superior corrosion resistance.

Bleach on Stainless Steel. What happens?

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