Galvanised Steel

Hot Dip Galvanised Steel

Hot Dip Galvanised is a form of galvanisation. It is the process of coating iron and steel with a layer of zinc by immersing the metal in a bath of molten zinc at a temperature of around 449 °C. When exposed to the atmosphere, the pure zinc reacts with oxygen to form zinc oxide, which further reacts with carbon dioxide to form zinc carbonate, a usually dull grey, fairly strong material that protects the steel underneath from further corrosion in many circumstances. Galvanised steel is widely used in applications where corrosion resistance is needed without the cost of stainless steel, and can be identified by the crystalline patterning on the surface.

Galvanised steel can be welded; however, one must exercise caution around the resulting toxic zinc fumes. Galvanised steel is suitable for high-temperature applications of up to 200 °C. The use of galvanised steel at temperatures above this will result in peeling of the zinc at the inter metallic layer. APAC recommends removing the galvanising with a grinder before any welding practices take place.

Like other corrosion protection systems, galvanising protects the steel by acting as a barrier between steel and the atmosphere. However, zinc is a more electro-negative metal in comparison to steel. This is a unique characteristic for galvanising, which means that when a galvanized coating is damaged and steel is exposed to the atmosphere, zinc can continue to protect steel through galvanic corrosion (often within an annulus of .5 mm, above which electron transfer rate decreases).