Guidelines for Rust Prevention, Storage, and Handling

There is a reference humidity level at which steel begins to corrode, known as critical humidity.

 In general:

• When the relative humidity exceeds approximately 70%, a thin moisture film can form on the steel surface, accelerating corrosion.

• When the relative humidity is kept below 60%, the likelihood of rust formation is significantly reduced.

Therefore, steel should be stored in a low-humidity environment and kept away from:

• Locations with large temperature fluctuations that may cause condensation

• Poorly ventilated or confined spaces

• Areas exposed to rain, moisture, or high humidity

If any packaging material is damaged, please repair it promptly to prevent moisture intrusion.

Even in low-humidity conditions, certain environmental components can accelerate corrosion:

• Chlorides in coastal environments (sea-salt particles)

• Acidic gases in industrial areas (e.g., hydrogen chloride, sulfur oxides)

• Hygroscopic gases that may exist near chemical storage areas

These substances can attract moisture from the air. As a result, corrosion may occur even when the humidity is below the critical level.

 More stringent anti-rust measures should be taken when storing steel in such environments.

Dust or foreign matter adhering to the steel surface may create a “local battery,” causing accelerated localized corrosion.

About the Local Battery Effect
When different areas of the steel surface develop a potential difference, a tiny galvanic cell may form. 

Metal ions in certain areas can dissolve more readily, resulting in electrochemical corrosion.

Common situations include:

• Dust, metal particles, or contaminants on the surface

• Tiny moisture-containing particles

• Small surface scratches

These conditions can break the protective anti-rust oil film, causing localized corrosion to occur rapidly.

To minimize risk, keep the storage environment clean, use the material promptly after unpacking, and avoid surface contamination.