What are the methods for preventing and removing rust from stainless steel industrial products?
Rust prevention and removal methods for industrial stainless steel products can be approached from multiple perspectives, including production process controls, routine maintenance, and post-rust treatment.
(I) Rust Prevention Methods:
The key to rust prevention lies in protecting the passivation layer on the stainless steel surface. This thin chromium oxide layer is fundamental to its corrosion resistance.
1. Selecting the Right Material: Choose different grades of stainless steel based on the operating environment. For example, in environments with high chloride content, choose 316L or higher grade stainless steel instead of 304.
2. Surface Treatment and Passivation: During manufacturing and installation, the stainless steel surface should be kept clean and free of debris such as iron filings, welding slag, and oil. After processing, pickling and passivation treatments should be performed to thoroughly remove free iron from the surface and restore any damaged passivation layer.
3. Routine Cleaning and Maintenance: Regularly wipe the stainless steel surface with clean water and a neutral detergent to remove dust, dirt, and potentially corrosive substances. Avoid using cleaning agents containing chlorine.
4. Avoid cross-contamination: During production, handling, and storage, stainless steel products should avoid direct contact with carbon steel, iron, and other products to prevent "free iron" from adhering to the stainless steel surface and becoming a starting point for corrosion.
5. Control the operating environment: Avoid prolonged exposure of stainless steel products to moisture, salt spray, or environments with high pH. If this is unavoidable, consider applying a protective coating, such as an anti-corrosion coating.
(II) Rust Removal Methods:
When rust appears on stainless steel products, appropriate rust removal methods should be selected based on the severity of the rust.
1. Physical Rust Removal
For light rust: Use a clean cloth and a stainless steel cleaner or polishing paste. Mild acids such as toothpaste and white vinegar can also be used, but the effect is limited.
For more severe rust: Use a nylon brush, stainless steel wire brush, or fine sandpaper (e.g., 240 grit or higher) to gently polish along the grain of the stainless steel. Remember not to use ordinary carbon steel wire brushes or sandpaper, as this can introduce iron filings into the stainless steel surface and cause new rust.
2. Chemical Rust Removal
Rust Removal Pastes or Rust Removers: Rust removal pastes or rust removers specifically formulated for stainless steel are commercially available, typically containing ingredients like phosphoric acid or citric acid. Apply the rust remover to the rusted area, let it sit for a while, and then rinse thoroughly with clean water. This method is suitable for large areas or deep-penetrating rust.
Acid Passivation: This is the most thorough rust removal and prevention method. Professionals will soak or spray the stainless steel surface with an acidic passivation solution (usually a mixture of nitric acid and hydrofluoric acid) to dissolve surface oxides and free iron, restoring a complete passivation layer. This method is typically used for large equipment or severely corroded areas and requires specialized expertise and protective measures.
Important Tips: Test Before Treatment: Regardless of the method used, test the stainless steel on a small, inconspicuous area first to confirm that there is no damage before proceeding to a larger area.
Passivation after Rust Removal: Physical or chemical rust removal damages the passivation layer on the stainless steel surface, reducing its corrosion resistance. Therefore, passivation treatment is necessary after rust removal to restore its corrosion resistance.
Avoiding Secondary Contamination: After rust removal, rinse thoroughly with plenty of clean water and wipe dry with a clean cloth to prevent residual chemicals or moisture from causing further rust.