White rust on galvanized steel is a common problem when it is stored in a humid and poorly ventilated environment. Generally, after long-term transportation, large amounts of white or grey powder will appear on the surface of the zinc layer, which is commonly referred to as white rust.
What Is White Rust on Galvanized Steel?
Zinc is a very active metal. When the surface of the galvanized layer comes into contact with moist air, it will first chemically react with the moist moisture to form a layer of porous and sticky corrosion products. Subsequently, zinc hydroxide will further react with carbon dioxide to form a thin, dense, and adhesive zinc carbonate corrosion product, which can prevent further corrosion of the coating. But electrochemical reactions will occur, resulting in the local white point-like powdery substance seen by the naked eye. That is white rust, a large amount of white or grey powder.
Galvanized Metal Steel Sheet
What Causes White Rust on Galvanized Steel?
1. High humidity;
2. Corrosion by acid gas or liquid.
3. The galvanized steel products are put into storage without drying in time.
Is White Rust Harmful?
Since the volume of metallic zinc increases by 3 to 5 times when it is converted into zinc oxide or zinc hydroxide, the white rust formed is larger in volume. As a result, white rust looks much more severe than it actually is, seriously affecting the appearance of the zinc coating. But in fact, white rust rarely affects the underlying zinc layer. Generally speaking, a small amount of white rust will not affect the anti-corrosion performance and the service life of the coating, and it will gradually disappear as the surface of the galvanized steel dries. However, if the galvanized metal is stored or transported in a humid environment for a long time, the white rust may not only affects the appearance of the product but also reduces its service life. You may better understand it when you know the rusting process of galvanized steel.