Does Salting Water Before it Boils Cause Pitting of Stainless Steel Cookware?

[Edward J]

Thing is, cookware mnfctrs have been warning consumers about putting salt in cold water and then turning on the heat for quite some time now.

 

 As a second year apprentice, back in the early 80's, we got new s/s pots and pans at work, each one had a warning sticker about this.  We were also informed at school about this.  Then again it wasn't Germany, but Luzern, Switzerland.

[fvandrog]

Did you see the article I linked above?

 

 

I did, and i have to admit, the main argument relevant for this discussion does not make a lot of sense to me:

 

Crevice Corrosion - this is a problem with stainless fasteners used in seawater applications, because of the low PH of salt water. Chlorides pit the passivated surface, where the low PH saltwater attacks the exposed metal. Lacking the oxygen to re-passivate, corrosion continues. As is signified by its name, this corrosion is most common in oxygen restricted crevices, such as under a bolt head.

Disolving kitchen salt (NaCl) in water does not change the pH in any way (sea water, if I recall correctly even has a slightly basic pH). So, this can not be the reason that salt causes damage of stainless steel cooking ware.

[paulraphael]

That's just one of many corrosion types. They key sentence is "Halogens penetrate the passive film of stainless and allow corrosion to occur. These halogens are easily recognizable, because they end with "-ine". Fluorine, chlorine, bromine, iodine and astatine are some of the most active."

 

Then if you look at the mechanism of pitting, a couple of paragraphs down, you can see how the process can take on speed.

 

As I said earlier, I don't believe the conditions under which this will occur come up much in normal cooking. Some people here (and some manufacturers) are warning that undisolved salt sitting in the bottom of a pan on the stove will allow it ... I'm not 100% convinced, and don't plan to test it, so I can't comment. But I don't leave salt or acid solutions in contact with my cookware for long periods, and don't use chlorine on them at all. The passivation layer that keeps stainless stainless is under a micron thick and vulnerable to many chemicals, and also to physical attack (abrasion). It's capable of renewing itself, but only under certain conditions and with plenty of oxygen present.

[Alex]

What is "quaternary ammonium?"

 

It's used for sanitizing all sorts of non-porous stuff (dishware, countertops, etc.). This is the very concentrated version I use. (There might be cheaper ones, but this is the only bottle I've needed so far.)

[fvandrog]

That's just one of many corrosion types. They key sentence is "Halogens penetrate the passive film of stainless and allow corrosion to occur. These halogens are easily recognizable, because they end with "-ine". Fluorine, chlorine, bromine, iodine and astatine are some of the most active."

Ah, okay. But indeed, that can only work if the salt has been dissolved, and there's free chlorine ions in the solution (and you'd need an oxidizing agent as well). In the case of undissolved salt, the chlorine is safely packed away within the crystals.

 

 

As I said earlier, I don't believe the conditions under which this will occur come up much in normal cooking. Some people here (and some manufacturers) are warning that undisolved salt sitting in the bottom of a pan on the stove will allow it ... I'm not 100% convinced, and don't plan to test it, so I can't comment.

I have often, unwittingly, done this experiment adding the salt long before the water reaches a boil. I generally use a stainless steel pot in the $30-$50 range for cooking pasta. Even after almost eight years I don't see any pitting whatsoever.

 

But I don't leave salt or acid solutions in contact with my cookware for long periods, and don't use chlorine on them at all. The passivation layer that keeps stainless stainless is under a micron thick and vulnerable to many chemicals, and also to physical attack (abrasion). It's capable of renewing itself, but only under certain conditions and with plenty of oxygen present.

I cook and clean -- no special treatment, but also not really challenging conditions.

[paulraphael]

It's used for sanitizing all sorts of non-porous stuff (dishware, countertops, etc.). This is the very concentrated version I use. (There might be cheaper ones, but this is the only bottle I've needed so far.)

 

Yes, I like these products ("quats") more than other sanitizers. Especially more than chlorine bleach, which wrecks towels and sponges and clothes, smells bad, and can theoretically attack stainless steel. 

 

Weak chlorine bleach sanitizers won't harm stainless in most kitchen situations ... it evaporates too quickly. I have a friend who brews beer, though, who tried to sanitize a stainless steel keg by filling it with a weak (swimming pool strength) bleach solution. He left it overnight, and by morning the solution had eaten all the way through and flooded his basement.

Edited April 2, 2014 by paulraphael (log)

[dcarch]

Of course I can be wrong on this, just because it is on the internet, or in manufacturer's instructions does not mean it is the truth.

 

For instance, the article Paulraphael linked to is totally wrong about the stainless steel used in the Chrysler Building, it is not 302 SS, it is called "Enduro KA-2" Steel.

 

I have put many "Dry Clean Only" fabric in regular cloths washer with no problem. I regularly put "Not Dishwasher Safe" items in dishwasher just the same.

 

Cookware manufacturers do not make the metals they use, they just buy them for their factories, and they do not generally hire scientists in writing their instruction manuals. I would not be surprised that either they play it safe, or just copy other manufacturers' manuals who buys the same metal for their products.

 

The bottom line is, of the 20 some odd stainless steel pots and pans in my kitchen, I can't seem to find any pitting. Some of them are more than decades old.

 

dcarch

[paulraphael]

dcarch, I agree that manufacturers' information is often dubious. For one example, you get wild stories from cast iron pan makers on how to season their products, few of them based on science.

 

But everything I've posted about stainless steel will be backed up by every metalurgical site you check. I promise. Salt is considered a corrosive agent to stainless steels, including the 300 series steels used in most cookware. The conditions and the relevance of this corrosivenes are what's at issue. My opinion is that it's not generally an issue in the kitchen—but that it could be if you did some things you probably shouldn't.

 

Edited to add:

Here's the most thorough explanation I've found anywhere. Aaronut's answer.

Edited April 3, 2014 by paulraphael (log)

[dcarch]

dcarch, I agree that manufacturers' information is often dubious. For one example, you get wild stories from cast iron pan makers on how to season their products, few of them based on science.

 

But everything I've posted about stainless steel will be backed up by every metalurgical site you check. I promise. Salt is considered a corrosive agent to stainless steels, including the 300 series steels used in most cookware. The conditions and the relevance of this corrosivenes are what's at issue. My opinion is that it's not generally an issue in the kitchen—but that it could be if you did some things you probably shouldn't.

 

Edited to add:

Here's the most thorough explanation I've found anywhere. Aaronut's answer.

 

Things can get confusing on discussing issues.

 

I actually am not disagreeing that salt can be corrosive to SS. I do understand very well the science of corrosion and electrolysis. I have done much electro-plating, electro-discharge machining, battery making, and studies in chemical qualitative analysis and equilibrium. Everything I have said, you will see, I am actually in agreement with you.

 

Under certain conditions and with some types of SS, which is not common in the kitchen environment, salt can produce chlorine, one of the halogen elements which can easily damage the oxide protective layer on SS. 

 

Regarding your link, It is important for me to point out correct information, which I feel is important for a public forum; I have worked in the Chrysler Building, that the Chrysler Building stainless steel has been in hostile NY weather and pollution for 80 some odd years, and not a detectable sign of wear. And I need to point out as well misinformation that, stainless steel is no where to be found except galvanized steel in the 77 floors of HVAC system, and air in an office building can not corrode SS.

 

dcarch

[Edward J]

The pitting in s/s cookware needs 3 elements in order to appear.  They are:

-Salt

-water

-heat

 

And by heat, we mean heat of around  25,000 btu's which is what typical commercial ranges put out.  It is the combination of all three, salt, heat, and water that pit any kind of metal in cookware.

 

 

 

I gave Mr. Carch a few days to research the use of s/s in hvac systems.  A simple google search with a common brand like Carrier would reveal that s/s is used in:

 

-Drain pans a.k.a. condensate pans

-heat exchangers

-hoses

-and with larger units of 50 tons and above, s/s cased booster coils.

 

Also remember that air conditioning is not just about blowing around air, it also is about removing moisture from the air.  Anybody who's ever had to deal with a leaky air conditioner or deal with soggy, stained ceiling tiles would have figured that out by now 

[Porthos]

I recently acquired a truly cheap S/S pasta pot. Unlike my older and definitely more expensive (but not WAY expensive) S/S pots this one is displaying pitting. I'm thinking I would lean toward small impurities that interrupt the the layer of passivation.

 

Way back when I designed the controller portion of some anodic protection equipment that maintained the passivation layer within the piping and heat exchangers of sulfuric acid manufacturing plants. I hadn't thought about that for a long time. I remember the engineering/construction company that designed the plants were VERY particular about the source of the materials that went into their plants.

[paulraphael]

 

Under certain conditions and with some types of SS, which is not common in the kitchen environment, salt can produce chlorine, one of the halogen elements which can easily damage the oxide protective layer on SS. 

 

Regarding your link, It is important for me to point out correct information, which I feel is important for a public forum; I have worked in the Chrysler Building, that the Chrysler Building stainless steel has been in hostile NY weather and pollution for 80 some odd years, and not a detectable sign of wear. And I need to point out as well misinformation that, stainless steel is no where to be found except galvanized steel in the 77 floors of HVAC system, and air in an office building can not corrode SS.

 

dcarch

It's not chlorine causing the corrosion, it's chloride ions, which are present whenever salt is in solution.

 

And regarding Edward’s point that the process requires more heat than what’s available in the kitchen, the type of reduction reaction we’re talking about is more active at low temperatures than high ones.

 

Which is one reason brining in the fridge is potentially more corrosive than simmering a salty stock. And it explains the conventional advice not to throw salt into cold water (although the conventional reasoning is incorrect … it’s got nothing to do with undisolved salt, which is harmless).

 

From the metallurgical sources I’ve found, there are two practices that are more likely than all the others to cause pitting in stainless: boiling a pan dry (especially if you don’t clean it immediately after), and storing it dirty (especially carbonized food stuck to it). 

 

From The Metals Handbook:

If debris of any kind is allowed to accumulate on the surfaces of stainless steel equipment, it will reduce the accessibility of oxygen to the covered areas and pits may develop in such locations because of the reduced oxygen concentration. [...] ...carbon deposits from heated organic compounds are typical examples of this source of [pitting] corrosion of stainless steels.

[boilsover]

Yes, undissolved salt can and does pit SS-lined cookware, even those lines using the best alloys.  It doesn't happen every time, but often enough to be a PITA.

 

Great examples of makers of good-quality wares who warn about this are Falk and All-Clad.  If you visit the competition over at Chowhound and search for "Falk", you will find several threads on this topic, and several posters whose warranty claims to Falk for salt-pitting have been denied because Falk specifically excludes salt pitting from its warranty.

[paulraphael]

Yes, undissolved salt can and does pit SS-lined cookware ...

See above ... it's actually disolved salt. Undisolved salt can't do anything to metal.

[budrichard]

Tempest in a tea pot!

I have a full line of Falk copper, never a pit, never a problem in about 20 years of ownership.

While my degrees are in Nuclear Engineering, my Master's study and research was in Metallurgy.

Salt(sodium hydroxide, NaOh) is corrosive. Stainless steel (SS) can corrode/stain/rust given water and oxygen.

Salted water should have no effect on a stainless lined pan/pot in normal usage.

What has been posted about impurities and inclusions in stainless steel coming out of China is correct.

I wouldn't give the matter another moments thought.-Dick

[Smithy]

Erm. budrichard, at the risk of being nitpicky here: while I agree that sodium hydroxide (NaOH) is a salt, it isn't the table salt under discussion here: sodium choride (NaCl). Is that really what you meant?

[budrichard]

NaCl

NaOH is a base.

-Dick