How to Maintain the Corrosion Resistance of Stainless Steel
What Is the Passive Layer and How Does It Form?
Stainless steels owe their corrosion resistance to a thin layer of chromium oxides on the surface, which forms spontaneously in the presence of oxygen, either during processing or accelerated through chemical passivation. To ensure maximum corrosion protection, the surface of stainless steel must remain clean and have adequate access to oxygen during operation. Oxygen combines with the chromium in the steel to form a layer of chromium oxides on the surface – a protective passive layer.
The Myth of “Stainless” Steel Being Corrosion-Proof
A common misconception is that stainless steel is resistant to all types of corrosion and that its surface does not require any maintenance. This misunderstanding may stem from the name itself – "stainless" steel – and a misinterpretation of this term. In English, stainless steels are called "stainless steels" - stain-less - meaning they corrode less, which clearly warns the user about the possibility of corrosion. Inexperienced users who have only used non-alloyed or low-alloy steels (black steels) often assume that stainless steels require no additional surface maintenance, taking their name "stainless" as a guarantee against corrosion under all conditions. Quite the contrary, to maintain their inherent corrosion resistance, stainless steels require periodic maintenance – primarily cleaning.
Why Surface Cleanliness Is Crucial
This is because their corrosion resistance depends on the mentioned thin passive layer on the surface. Any contamination, deposits, embedded particles of foreign materials, or accumulating ions that destroy the passive layer will reduce this resistance. This is especially important for elements operated in environments containing chloride salts, sulphides, or other corrosive metal materials. In such environments, the stainless steel surface may discolour, become covered with corrosion products, and begin to corrode itself.
Common Mistakes in Cleaning and Maintenance
Stainless steel requires regular maintenance and cleaning – this should be noted especially in the warranty conditions of manufactured products, indicating to the user what cleaning methods should be used, how often they should be performed, what agents should not be used (steel-bristled brushes; cleaning agents containing harsh abrasives; cleaning agents containing: chlorides, fluorides, bromides, iodides, and acids containing these compounds; bleaches and hypochlorite-based agents; products dedicated to cleaning silver), and what agents can be used (synthetic fibre brushes; gentle fabrics; alkaline agents; agents based on phosphoric acid, citric acid; organic solvents; agents dedicated to chrome and stainless steel surfaces). This approach is to create and maintain favourable operating conditions so that stainless steel does not corrode over a long period.
Recommended Cleaning Agents and Techniques
Below are some recommendations for cleaning and maintaining stainless steels and critical factors to be aware of.
Cleaning industrial concrete floors: avoid contact with concrete cleaning detergents (contain chlorides), protect from contact or intensively wash the surface with clean water.
Cleaning steel may require the use of harmful chemicals: follow the product's safety instructions (health hazard) and usage instructions (possible corrosion), do not exceed the permissible contact time of the medium with stainless steel, always rinse thoroughly with clean water after use.
Do not clean surfaces directly in the sun or at too high a temperature.
When cleaning stainless steel:
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never use highly abrasive materials, steel wool.
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never clean with inorganic acids (especially hydrochloric acid or bleaches), bleaches containing sodium hypochlorite, which can cause surface discoloration and pitting corrosion,
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never allow contact between stainless steel and non-alloy steel (particles of these steels will undergo accelerated corrosion on the surface of stainless steel).
How to Remove Different Types of Contaminants and Rust
Routine cleaning:
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rinse off permanent dirt and contaminants with clean water, wipe the surface with a soft cloth.
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for heavier soiling - mild soap or detergent (cleaning ammonia, baking soda, vinegar, citric acid) and a soft nylon brush.
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rinse thoroughly after cleaning.
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clean elements at least once a year (more often in coastal and industrial areas).
Cleaning contaminants from non-alloy steel (black steel) and iron particles:
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A solution of oxalic acid can be used for cleaning, applied to the surface with a soft cloth. Leave on the surface for a few minutes (do not rub) to dissolve contaminants. Rinse thoroughly with water.
Light rust:
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Household cleaners dedicated to stainless steel containing calcium carbonate or citric acid. Rinse thoroughly with water.
Moderate discoloration:
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Clean with phosphoric acid-based agents or a 10% solution of phosphoric acid. Spray the surface and wait 30–60 minutes (or as recommended by the manufacturer). After cleaning, neutralize the acid with diluted ammonia or a mild alkaline detergent. Rinse thoroughly with water.
Heavy rust:
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Use professional service providers or dedicated products for etching and passivating steel. Always rinse the surface thoroughly with water after treatment.
Stainless steel is an exceptional material that requires regular maintenance to retain its corrosion-resistant properties. With proper care, stainless steel can last for many years, maintaining its aesthetic appearance and durability.
For the highest quality stainless steel products and more maintenance tips, visit StainlessEurope – your trusted online supplier of stainless steel products.