How Galvanized Steel Prevents Rust
Galvanized steel is steel that has a protective layer of zinc applied to its surface. This zinc coating performs a dual function in preventing rust:
- Barrier protection: The zinc coating acts as a physical barrier, preventing moisture and oxygen from reaching the steel underneath.
- Sacrificial protection: Zinc is more reactive than steel. This means that if the coating is scratched or damaged, the zinc will corrode first, "sacrificing" itself to protect the steel underneath from rusting. This is also known as electrochemical protection.
Factors that cause galvanized steel to rust
Although very effective, zinc coatings are not permanent and will break down over time, especially in certain environments. Factors that can accelerate corrosion include:
- High humidity: Environments with humidity over 60% can cause zinc coatings to break down more quickly.
- Salt exposure: Salt in the air or water in coastal and marine environments is highly corrosive to zinc coatings.
- Pollution: Industrial and urban areas with high levels of sulfur dioxide and other pollutants can accelerate corrosion.
- Coating damage: Scratches, cuts, or other mechanical damage can compromise the protective zinc layer and expose the steel to the elements.
- Chemical exposure: Exposure to strong bases, such as wet cement or plaster, can also damage the zinc coating.
How long does galvanized steel last?
The rust protection life of galvanized steel depends largely on the thickness of the zinc coating and the corrosiveness of the environment it is in. In less corrosive environments, hot-dip galvanized coatings can last up to 75 years or more. Even in harsh conditions, they can last far longer than untreated steel. For example, in harsh soil environments, they can last 35 to 50 years.
