Metal Casting

How to Clean Stainless Steel and Prevent Corrosion

An image of a stainless steel bollard being cleaned

Protect Stainless Steel from Rust with Proven Cleaning Methods and Passivating Treatments

An image of a stainless steel bollard being cleaned
Maintaining stainless steel products clean and debris-free extends their service life significantly.

Stainless steel is known for its corrosion resistance, but regular cleaning and maintenance are essential to preserve its appearance and functionality. Without proper care, it can suffer from oxidation, corrosion, rusting, or staining, particularly in harsh environments. Frequent mechanical damage can also accelerate its degradation. Learn effective cleaning methods and passivating treatments to protect stainless steel surfaces and ensure their longevity.

A man cleaning a stainless steel bollard
Stainless steel applications require regular cleaning and maintenance to protect from oxidation, corrosion, rusting, and staining.

Understanding the Passive Layer in Stainless Steel

To understand the importance of keeping stainless steel clean, you must first grasp how the passive layer works to protect it from the elements. All stainless steels contain at least 10.5% chromium by weight. This chromium forms a protective shield known as the passive layer, which prevents corrosion. The higher the chromium content, the greater the corrosion resistance. Stainless steel rusts when the passive layer is damaged, and there is insufficient chromium to reform it.

Formation and Function of the Passive Layer

The passive layer forms when chromium in stainless steel reacts with oxygen, creating a protective barrier that prevents further oxidation. In comparison, ordinary carbon steel forms ferric oxide when exposed to oxygen, which does not provide continuous protection and leads to rusting.

Self-Repair Mechanism of Stainless Steel

The passive layer of stainless steel is self-repairing. If it is damaged, the chromium in the exposed stainless steel reacts with oxygen to form new chromium oxide. As long as there is sufficient chromium present, the chromium oxide layer will continue to reform and protect the stainless steel surface.

Iron and carbon steel particles on a drill
Contamination occurs when stainless steel is subject to sparks or particles from nearby welding, cutting, drilling, or grinding of carbon steel.

Causes of Stainless Steel Corrosion

While there is a common misconception that stainless steel is impervious to corrosion, it is still possible due to various factors. Chromium protects stainless steel if the localized concentration is 12% or higher. Anything reducing the localized chromium concentration below the 12% threshold will cause staining or rust. Common causes of stainless steel corrosion include:

  • Chlorides: Chromium oxide is particularly vulnerable to chlorides. Corrosion is accelerated in coastal areas with salt-spray exposure and in areas where de-icing salts are used during winter. Components for the chemical and food industries have high chromium content to compensate for regular exposure to chlorine, salt, and other corrosive substances.
  • Acids: Strong acids destabilize the passive layer. Hydrochloric and sulfuric acids can cause general surface corrosion. Hydrochloric acid is used in plastic production and descaling agents, while sulfuric acid is used in mineral processing, oil refining, and wastewater processing.
  • Iron and Carbon Steel Particles: Stainless steel corrosion can also be triggered by contact with iron or carbon steel particles. Trace particles from iron or carbon steel will rust stainless steel surfaces. If left unattended, rust spots may compromise the chromium oxide surface and evolve into localized corrosion such as pitting. Contamination occurs when stainless steel is subject to sparks or particles from nearby welding, cutting, drilling, or grinding of carbon steel.
  • High Temperatures: A less common form of rusting occurs after the stainless steel has been exposed to very high temperatures (750–1550°F). During processes such as welding, sensitization can occur, where the carbon and chromium bond to form carbides, causing the grain boundaries to become chromium deficient and the passive layer to become discontinuous. However, the damage can sometimes be mitigated with heat treating.
Stainless steel being welded
Sensitization in welding applications causes grain boundaries to lose chromium content and the chromium oxide layer becomes discontinuous.

How to Handle Stainless Steel

Handling stainless steel properly is crucial to extend its service life and maintain its pristine condition. Here are the best practices to follow when working with stainless steel:

Best Practices for Handling Stainless Steel

  • Always wear clean gloves: Prevent fingerprints and other contaminants.
  • Use stainless steel tools and components: This avoids contamination from other metals.
  • Avoid contact with carbon steels or iron: These can cause corrosion.
  • Do not weld, cut, drill, or grind carbon steel near stainless steel: Prevent cross-contamination.
  • Avoid contact with concrete detergents: These can be harsh and corrosive.
  • Avoid contact with chloride solutions: These can cause pitting and corrosion.
  • Do not use steel wool or other abrasive scrubbing pads: These can damage the surface.

Common Mistakes to Avoid

The most common mistake when handling stainless steel is using corrosive products to clean it. Never use the following products on stainless steel surfaces:

  • Chloride cleaners
  • Abrasive cleaners
  • All-purpose cleaners
  • Chloride bleach

How to Clean Stainless Steel

Stainless steel must be cleaned regularly to preserve the metal’s integrity and maintain a pristine appearance. With proper care and by selecting an appropriate grade, stainless steel can not only be protected from corrosion but also provide a long service life. Neglecting maintenance can lead to the accumulation of corrosive substances on vulnerable surfaces.

Routine Maintenance for Stainless Steel (Recommended Every 6 Months)

  1. Gently scrub away any accumulated dirt or grime using a soft nylon brush.
  2. Cleanse the surface using a mild soap or detergent that is safe for stainless steel.
  3. Thoroughly rinse the stainless steel with clean water to remove any residue.
  4. Ensure the stainless steel is completely dry. Use a soft cloth, disposable wipe, or even an air blower to achieve a dry surface.

Stainless steel care and maintenance may require the use of harmful chemicals. Follow all safety instructions provided with cleaning or polishing agents. Ensure personal protective equipment is worn in accordance with occupational health and safety guidelines.

Advanced Stainless Steel Cleaning Techniques

When stainless steel becomes extremely dirty with signs of surface discoloration or corrosion, routine cleaning may no longer suffice. Use the following methods for specific types of damage:

Fingerprints on a stainless steel railing
  • Clean with soap or detergent and warm water.
  • Commercially-available solutions or hydrocarbon solvents can also be used.
Oil and grease marks on stainless steel
Oil and Grease Marks
  • Use isopropyl alcohol, acetone, or methylated spirit.
  • Apply solvent several times with a clean, non-scratching cloth until all marks are removed.
Burnt-on stain on a stainless steel pot
Burnt-on Stains
  • Soak in hot water and diluted ammonia or detergent.
  • Remove grime with a nylon brush.
  • If needed, use a fine abrasive powder but be careful not to scratch polished surfaces.
  • Rinse thoroughly with clean water.
Coffee stains on stainless steel
Discoloration, Coffee, and Tea Stains
  • For discoloration, use mild, non-abrasive cleansers. Apply with a soft cloth or sponge and rinse thoroughly with clean water.
  • For coffee stains, soak in a sodium bicarbonate solution (baking soda and warm water).
  • For tea stains, soak in a sodium carbonate solution (washing soda and warm water). If the object is too large to soak, use a sponge or a soft cloth.
Rust stain on stainless steel bollard
Localized Rust Stains
  • Use a soft cloth to apply an oxalic acid solution.
  • Leave the solution on the surface for a few minutes to dissolve contaminating particles.
  • Rinse away all residual solution with clean water.
Limescale on stainless steel
Limescale, Cement, and Mortar Splashes
  • For limescale, dilute one part vinegar in three parts water and apply with a nylon brush.
  • For cement and mortar splashes, rinse splashes off immediately. Use a 10%–15% phosphoric acid-based solution in warm water. Spread cleaner evenly, wait 30–60 minutes, then neutralize the acid with an alkaline cleaner or diluted ammonia. Rinse with clean water.
Graffiti damage on stainless steel
  • Use biodegradable graffiti-cleaning sprays or wipes.
  • Avoid using knives or hard scraping tools to prevent damage to stainless steel surfaces.
Stainless steel with heat stains
Heat Stains
  • Use a domestic metal polish (chrome polishes for automotive parts are widely available and effective).
  • Treat the entire stainless steel surface to avoid discolored patches.
Dent marks on stainless steel
Structural Damage
  • Structural damage includes any visible dents, cracks, and breaks.
  • Heavily damaged products should be removed from service until a repair or replacement can be made.
  • To prevent worsening of damage, any significant rust should be removed as soon as possible.
Corrosion on a stainless steel bollard
  • For minor corrosion, use an all-purpose lubricant, such as WD-40, to wipe the affected area. Rinse thoroughly with clean water.
  • For moderate corrosion, use a phosphoric acid-based stainless steel cleaner such as E-NOX CLEAN. Spread the cleaner evenly, leave on for 30–60 minutes, then neutralize the acid with a spray-on alkaline cleaner such as UNO S F. Wipe the surface clean with a paper towel. Rinse thoroughly with clean water.
  • For severe corrosion, consult a professional service provider. Once treated, stainless steel can be passivized with mild nitric acid.

Passivation Procedure

Passivation maximizes the inherent corrosion resistance of a stainless alloy. Ideally, the passive layer will develop immediately after machining or passivation to completely cover the stainless steel surface. In reality, particles and contaminants are likely to adhere to the surface. If they are allowed to remain, these foreign particles reduce the effectiveness of the original protective film. Passivation is needed to maximize the natural corrosion resistance of stainless steel and remove surface contamination.

A two-step passivation procedure provides the best possible corrosion resistance:

  1. Cleaning: The stainless steel part must be thoroughly cleaned. Stainless steels cannot be passivated unless the surface is clean and free from contamination and scale. In extreme cases, foreign matter may have to be removed by grinding or mechanical abrasion, or by pickling before passivation can take place.
  2. Passivating Treatment: The stainless steel part is immersed in a passivating acid bath. Any one of three passivating approaches can be used: nitric acid passivation, nitric acid with sodium dichromate passivation, or citric acid passivation. The passivation treatment varies depending on chrome content and machinability characteristics of the stainless steel grade, as well as the prescribed acceptance criteria.

Extending Stainless Steel’s Lifespan

Proper routine care and specialized cleaning for more serious problems can extend stainless steel’s lifespan and ensure that applications operate smoothly. Although stainless steel’s built-in chromium content works to guard against corrosion, relying on this alone is insufficient. Exposure to chemical solutions, weathering, salt, or mechanical damage—all contribute to the need for routine passivating treatment. Passivation procedures and correct cleaning methods help stainless steel continue to shine as one of today’s most versatile materials in the commercial and industrial world.