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Cleaning stainless that has been exposed to chlorine for a long time.


Hot Rolled
May 14, 2011
Bridgeton NJ
So I have a customer who has a room full of stainless that has been exposed to an open tank of chlorine for a couple of years. I am being asked to restore the stainless finish. They don't want me to use sanding as a reason due to the room it is in.

I don't really use chemicals for cleaning or passivating so I am asking for help is what I could use.

There are 3 tanks that are 4,000 to 5,000 gallons. A few square tube frames, smaller tanks, and piping.

The corrosion isn't pitting or anything yet, but it doesn't seem that far off in some spots.
Chlorine attacks chromium..........I suspect you will find metallurgical damage to the stainless.............hexavalent salts and all that ..........I also suggest you be sure you arent the one in a thousand who is sensitized to chromium salts .........the sensitivity can kill ,as very few doctors recognize it until the autopsy.
You will have to mechanically restore the surface, then repassivate it. Thankfully, chlorine isn't a precursor to hexavalent salts, but the mechanical work you'll have to do is.
What happens to stainless steel when exposed to chlorine?

In media containing the anion chloride, stainless steels may suffer mainly localized corrosion (for example, pitting). In this case, the corrosive attack will cause gaps in the metal passivation film

only fix is to replace it. or mechanical means but that is already a no.
Dilute nitric acid is the stuff for passivating stainless steels (and aluminium, for similar reasons) 2molar/10% concentration should be enough. 5molar will be quicker and last longer.

Note:- I'm not a chemist and don't play one on TV. Just going by what the metallurgists at work told me when I had a similar problem a few decades ago.
It is a good customer, and I have already ran into this issue at another customer. They used a different company and they used s chemical to remove the corrosion, not 100%, but like 95%.

Scotch Brite will spread the issue if we don't passivity it quickly.

Would a passivation machine like a Walter surfox or whatever it's called work to remove it?

I haven't said yes or no to the job.
It wouldn't hurt to give Citrasurf a call and see what they have to say. If they have an answer, it will be safer than other alternatives.

Also, try the Alconox people. They have some acid cleaners that might be useful.
We used to get rust spotting on stainless from steel particles floating in the air ......the stainless cleaner was a mix of 30%strength nitric acid with 3% of hydroflouric acid ,as a gel .
I just found out today that the room only started rusting because I fixed the belt a few weeks ago, but it was broken for a few months. Crazy how that happened. Anyways, now that their maintenance created this problem, I told then we would need some time with the main doors open. The customer is also talking to another company which is I would perfer.