Galvanized steel, known for its protective zinc coating, is commonly used in various applications due to its durability and resistance to corrosion. However, despite the benefits, galvanized steel can still be susceptible to corrosion over time. Understanding the causes of this corrosion process is essential for proper maintenance and extending the lifespan of galvanized steel products.

Corrosion Process of Galvanized Steel

The corrosion of galvanized steel begins with the oxidation of the zinc layer. Initially, this oxidation forms “white rust” on the surface. Over time, if the corrosion progresses, the white rust reacts with carbon dioxide and other gases in the atmosphere, turning into “black spots.” If left unchecked, this process continues and the zinc layer degrades, exposing the underlying steel to oxidation, which results in “red rust.” Once the steel substrate starts oxidizing, corrosion accelerates, significantly reducing the service life of galvanized steel.

Factors Influencing Galvanized Steel Corrosion

1. Relative Humidity
   The moisture content in the air is a key factor affecting the corrosion rate of galvanized steel. At lower relative humidity levels, corrosion is slow. However, as the humidity increases, the corrosion process speeds up, especially when it reaches a certain threshold, causing a more rapid deterioration of the zinc coating.
2. Temperature
   Temperature plays a crucial role in the corrosion rate. For every 10°C rise in temperature, the corrosion rate roughly doubles, especially when the metal is exposed to certain humidity levels. Fluctuations in temperature, such as large day-night or indoor-outdoor temperature differences, lead to condensation on the metal surface. This condensation can exacerbate rusting, particularly in areas with high humidity, such as hot, rainy, or foggy environments.
3. Oxygen
   Oxygen in the atmosphere is another major contributor to metal corrosion. The thin water layer on the steel surface allows oxygen to easily dissolve and penetrate, accelerating the corrosion process. This continuous presence of oxygen is critical for rust formation.
4. Pollution Factors
   Environmental pollution also accelerates the corrosion of galvanized steel. Airborne pollutants or contamination on the metal surface can lead to rapid corrosion, even at lower relative humidity. As the humidity level increases, the corrosion rate intensifies, especially when the surface is not properly cleaned.

How to Prevent Galvanized Steel Corrosion

To maintain the integrity of galvanized steel, it’s essential to mitigate the factors that lead to corrosion. Proper coating, regular maintenance, and environmental control can significantly reduce the impact of corrosion. In addition, manufacturers must ensure that galvanized steel products undergo thorough cleaning and proper surface treatment before use, especially in areas with high humidity or pollution.

Conclusion

Galvanized steel offers excellent corrosion resistance, but its lifespan can be compromised by environmental factors such as humidity, temperature fluctuations, oxygen exposure, and pollution. By understanding these factors and taking preventive measures, the service life of galvanized steel can be extended.