Hot-Dipped Galvanized Corrosion Protection and Zinc Patina

Freshly galvanized steel progresses through a natural weathering process. During the first few weeks after an article has been galvanized, it develops a natural protective patina. If allowed to develop properly, the patina itself provides a corrosion protection layer for the active zinc metal.

The formation of the zinc patina begins with the development of a thin layer of zinc oxide particulates on the freshly coated surface. These particulates react with water, from rainfall or dew, to form a porous, gelatinous zinc hydroxide. During drying, this product reacts with carbon dioxide present in the atmosphere and converts into a thin, compact and tightly adherent layer of corrosion products consisting mainly of basic zinc carbonate. The rate of patina formation varies according to the environmental conditions. Typically, it takes approximately 6-12 months to fully develop.

Handling and storage conditions can inhibit the formation of the patina. Storage areas that are high in humidity and lack air circulation tend to promote excessive growth of zinc oxide and zinc hydroxide. Adequate ventilation must be provided so that the build-up and retention of excessive water on the surface of the galvanized steel are avoided.