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Bruce Bruce is offline
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First recorded activity by BoatBanter: Mar 2007
Posts: 117
Default Stainless Steel "rust" marks on paint

On Wed, 28 Mar 2007 15:03:32 -0500, Don W
wrote:

Bruce wrote:

snip--Eric's good primer on pickling and passivation of austentetic stainless steels
Pickling and passivation


Thanks for quote. I knew that stainless reacted with oxygen to form a
non-corrosive surface and that unless you had a flow of water the lack
of dissolved oxygen might result in crevice corrosion but somehow had
never related it to pasivating. I'll now use at least come nitric acid
as an oxidizing agent.

Bruce in Bangkok
(brucepaigeatgmaildotcom)


Bruce,

I'll try to steer you to looking into stainless
steel passivation using strong citric acid (ie
Citrisurf, etc.) once more. I've not time to
provide the relevant links at the moment.

Use nitric acid if you like. It works also,
although not as well as citric acid according to
various studies. It is also much more hazardous
to transport and dispose of. Citric acid can be
diluted and legally flushed down the drain.

Citric acid passivation for SS is fairly new
technology, and Nitric acid is the traditional way
of doing it. Citric acid can also be used with a
power supply to electropolish stainless steel.

The people who turned me on to the citric acid
passivation do a lot of industrial and food grade
stainless welding and have switched over.

Good luck,

Don W.


Don't get me wrong, I really appreciate your information. My reply was
supposed to indicate that while I knew that stainless needed a certain
amount of oxygen to be "stainless" I had never related that
information to the passivation process.

Citric acid may prove a problem though as I live in Thailand thousand
and some things are just not available. Add to this the (sometimes)
problem with translating technical terms and life sometimes becomes
very frustrating. However, when I return to Bangkok I'll stop by my
chemical supply place and see what is available.

One nice thing about Thailand is that it is still primitive enough
that people actually want to sell you things. You go to a large
chemical supply house and say, "I need a liter of a 6-1/3% solution of
nitric acid and distilled water and they never blink an eye. Just
apologize for not being able to hand it to you straight away and ask
you to come back tomorrow morning, about 09:00.


Bruce in Bangkok
(brucepaigeatgmaildotcom)

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