Salt's Corrosive Impact On Stainless Steel Cookware

Stainless steel pans are a popular choice for home cooks and professionals alike, thanks to their durability and ease of care. However, one common mistake that can shorten the lifespan of your stainless steel pans is adding salt to cold water. This can lead to pitting, a form of rusting where the protective layer of chromium oxide breaks down, resulting in tiny circular indents on the surface of the pan. To prevent pitting, it is recommended to only add salt to water once it has started boiling, ensuring the salt dissolves immediately.

Pitting corrosion

Chlorine and chloride salts are responsible for metal pitting on stainless steel. They cause a breakdown of the passive chromium oxide layer on the metal, and once the pitting starts, it can spread rapidly. Substances that contain chlorides, such as sodium chloride (common table salt), can cause pitting. Simply filling a stainless steel pot with salty water is likely to cause pitting, even if the water is not heated.

The pitting reaction requires oxygen, so it can be avoided by adding salt only after water has come to a boil. At boiling temperature, there is not enough oxygen in the water for the reaction to occur.

While pitting corrosion can affect the performance of stainless steel cookware, it does not render the pots and pans unsafe for food use. However, it is important to note that pitting cannot be repaired, and once it starts, it may not be long before the cookware develops pinholes and becomes unusable. Therefore, it is crucial to take preventive measures, such as adding salt to boiling water, to avoid pitting corrosion in the first place.

Chlorine and chloride

Chlorine is a powerful oxidising agent that is usually found as a gas. In its gaseous form, chlorine is not typically aggressive towards stainless steel. However, when chlorine is dissolved in water, it can become corrosive.

Chlorine readily forms chlorides when in contact with gases such as methane, hydrogen sulphide, and ammonia. These reactions can form hydrochloric acid (HCl). When dissolved in water, chlorine forms a highly corrosive mixture of hydrochloric and hypochlorous (HOCl) acids.

Additionally, chlorine can aid in the oxidation of dissolved gases like sulphur dioxide (SO2), leading to the formation of sulphuric and hydrochloric acid in water. These oxidising properties contribute to the aggressive nature of chlorine in water.

When chlorine is in contact with water or dissolved in water, it can potentially cause localised crevice and pitting corrosion in stainless steel. This is particularly evident in water treatment applications. Condensates formed over chlorinated water in storage tanks have been associated with staining or pitting of stainless steels.

The extent of corrosion caused by chlorine also depends on other factors. Higher temperatures, combined with higher chloride levels and lower pH, can exacerbate the corrosion of stainless steel.

To mitigate the effects of chlorine on stainless steel, it is recommended to maintain proper ventilation and avoid prolonged exposure. For 316 type stainless steel items, a maximum of 15-20 ppm (mg/lt) of 'free' chlorine is advised for a maximum of 24 hours, followed by a thorough flush with chlorine-free water.

Regarding salt and stainless steel pans, it is important to understand that salt is primarily composed of sodium chloride. When salt is added to water in a stainless steel pan, the chloride ions can lead to pitting corrosion. This occurs when the protective layer of chromium oxide breaks down, resulting in tiny circular indents on the stainless steel surface. However, this corrosion can be minimised by adding salt to the water after it has started boiling, as the salt will dissolve immediately instead of settling at the bottom and interacting with the metal surface.

Boiling water first

To avoid this, only add salt to your water once it has started to boil. This ensures that the salt dissolves right away rather than settling at the bottom of the pan and interacting with the surface metal.

If you are cooking pasta, wait to add salt until the water is already boiling. This will help to extend the life of your stainless steel pans and keep them in pristine condition.

In addition to salting your water at the right time, there are other steps you can take to care for your stainless steel pans. Always allow your pan to cool down before cleaning to avoid warping. Hand-washing is typically the best way to clean stainless steel pans, and you should use non-abrasive tools and cleaners to avoid damaging the surface. For stuck-on food bits, fill the pan with soapy water, bring it to a boil, and scrape with a spatula or wooden spoon.

By following these simple tips, you can effectively clean and maintain your stainless steel pans, ensuring their longevity.

Cleaning stainless steel

Stainless steel pans are a great choice for cooking as they are relatively easy to care for and are non-reactive with acidic foods. However, without proper cleaning and care, they can become pitted or rusted. Here are some tips for cleaning and maintaining your stainless steel pans to keep them in the best shape possible:

General Care for Stainless Steel Pans:

• Always let your pan cool down before cleaning to avoid thermal shock, which can cause warping.
• Prevent water spots and discolouration by drying pans immediately after washing.
• Avoid using cold water on a hot pan to prevent warping and disfiguration.
• Avoid harsh scrubbers or cleaners, such as steel wool, that can scratch stainless steel surfaces.
• Avoid cleaning with salt or saltwater, as this can lead to pitting.
• Bring refrigerated foods to room temperature before adding them to the pan to prevent sticking.
• Preheat your pan before adding oil, and wait until the oil is hot before cooking.
• When cooking pasta, wait to add salt until after the water is boiling to prevent pitting corrosion.

Removing Stuck-On Food:

• Use a spatula or paper towel to remove excess oil.
• Loosen stuck-on food with a long-handled dish brush.
• For lighter stains, scrub with a soft sponge or scouring pad, dish soap, and hot water.
• For tougher stains, use a commercial cleaner like Bar Keepers Friend or baking soda.
• For burnt-on food, fill the pan with soapy water, bring to a boil, and scrape with a spatula.

Removing Discolouration:

• For rainbow-coloured discolouration caused by overheating, splash some vinegar in the pan and wipe with a soft sponge before rinsing and drying.
• For white, cloudy residue caused by hard water, boil a mixture of one part vinegar to three parts water, let it cool, then wash with soap and water.

Chromium oxide

In the context of stainless steel cookware, the protective layer of chromium oxide can break down due to a process called pitting. Pitting is a form of rusting where the stainless steel surface is damaged by salt. This typically occurs when salt is added to cold water in the pot, allowing the salt to settle at the bottom and interact with the metal surface. However, salting at the right time, such as after the water has started boiling, can prevent pitting by ensuring the salt dissolves immediately.

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