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How can stainless steel corrode?

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Q. How exactly can stainless steel corrode?

Liljana E.
student - Perth, WA, Australia


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Please tell us what grade you are in and what you know about stainless steel, and then we may be able to help, Liljana. Sorry, but the answer must be very different for elementary school students vs. college students, as I'm sure you can appreciate.

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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Also, please include what you mean by corrosion. It means different things to different people.

James Watts
- Navarre, Florida

misc. plating stuff
For Sale cheap



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All "stainless" steels can corrode under the wrong conditions. Many companies, in fact, do not call them stainless steels, but "corrosion resistant" steel. Remember that most of the metal is still iron and can corrode or rust depending on how much stress it is exposed to. One of the worst things you can do to stainless steel is expose it to chlorides. The better grades can withstand a lot of abuse, but most grades can eventually fail when exposed to chlorides in bad atmospheres.

Some grades of "stainless" steel have very poor resistance to corrosion, if fact. They are marginally better than carbon steel, but when correctly hardened and passivated or electropolished can give fairly good performance. The grade of steel must reflect the exposure conditions and performance required.


Lee Kremer
Stellar Solutions, Inc.

McHenry, Illinois


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Liljana,

Stainless can be corroded, ie. attacked, depleted and dissolved in the presence of some acids ... but even seawater, which contains salt, as you know, can attack some of the various grades of stainless especially around the welds.

Why the question? What type of stainless are you talking about? Or is this just idle curiosity?

freeman newton portrait Freeman Newton
- White Rock, British Columbia, Canada

freeman newton died

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Regarding the corrosion of stainless steel, I would say stainless steel exhibits good corrosion qualities because of the chromium layer formed on it and this chromium which also contributes to one of its major constituents when exposed to brine, or calcium chloride is corroded (rusting can also be the initial outcome). Acidic attack which can include Hydrofluoric acid, Hydrochloric acid, Phosphoric acid & sulphuric acid can also do the job. Please don't hesitate to ask -- I know a lot about all this.

Shehzad Saleem Khan
- Germany


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Q. What is Phosphoric acid's effect on Stainless steel 304L in the case where concentration of phosphoric acid is 75%?
In case corrosion takes place, do you have any advice to keep the pipelines maintained and protected?

Hanydeleted
- Egypt


August 15, 2008

We have shifted to a new house that was built last year. all the sanitary fittings are of stainless steel (I checked it with a magnet, not attracting). however, with exposure to underground water it is rusting. even some utensils show some rust. I used to think that SS does not rust. any idea why? by the way, water is very hard and we have to use a Reverse Osmosis unit before drinking\cooking. also, corrosion starts within a month of exposure

AMIT TALUKDAR
- New Delhi, India


September 17, 2011

I purchased Bon Chef lidded coffee pots (stainless steel) from a restaurant supply store. The purpose is to use them at the preschool for kids to pour water from. We filled them with water around 8 am and by noon, at least one showed brown circular spots on the inside bottom of one. Also a ring of brown spots along the bottom wall. We filled another 3 during the afternoon between 1 pm to about 3 pm, again they all showed various signs of rust. I'm not sure about the morning. But in the afternoon I was using filtered water.

Why are they doing this, especially for an item that came from a restaurant supply store?

Crystal Nie
- California USA

December 7, 2012

Q. Hi all,

Sorry to ask such a silly question, but I need someone who really knows steel to answer it:

Does orange juice eat through stainless steel?

Orange juice contains a small amount of citric acid which is corrosive to some metals, but is it strong enough? I would really appreciate a little background info on whatever you answer, for example how long it might take or what grade of stainless steel would or would not corrode, and how much corrosion would occur, i.e. would it just tarnish the surface or would it eat right through?

Any help gratefully received, thanks in advance.

Keir Ritchie
- London, UK


December 10, 2012

A. Hi Keir.

It would certainly not "eat right through", but it's probably more likely to very slowly dissolve stainless over a period of many months or years than to form a layer of tarnish on it.

Even though stainless steel may not be 100.0000% resistant like some plastics would be, electropolished type 316SS is widely used in food and pharmaceutical factories because it is so smooth that it can be cleaned very well to prevent cross contamination (which can be a bigger problem than very slow corrosion).

I don't have experience in orange juice factories, so I can't answer really knowledgeably, but based on more general experience I would expect that if the tanks are used for nothing else, they would probably be plastic or lined with plastic, but the valves and piping, etc. would probably be stainless steel.

Around the house, stainless steel "juicers" would be common because plastic isn't strong enough. And stainless is commonly used for measuring cups, spoons, bowls, etc., that might be used for orange juice.

Regards,

pic of Ted Mooney Teds signature
Ted Mooney, P.E. RET
finishing.com
Brick, New Jersey

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