Galvanisation (or galvanising as it is most commonly called in that industry) is the process of applying a protective zinc coating to steel or iron, to prevent rusting. The most common method is hot-dip galvanising, in which parts are submerged in a bath of molten zinc.
On immersion in the galvanising bath the steel surface is completely covered by the molten zinc, which reacts with the steel to form a series of zinc-iron alloy layers, producing a uniform coating. The thickness of these layers is determined principally by the mass of the steel being galvanised.
However, the protection provided by hot-dip galvanising is insufficient for products that will be constantly exposed to corrosive materials such as acids, including acid rain in outdoor uses. For these applications, more expensive stainless steel is preferred.
Galvanising protects the base metal in three ways:
- It forms a coating of zinc which, when intact, prevents corrosive substances from reaching the underlying steel or iron.
- The zinc serves as a sacrificial anode so that even if the coating is scratched, the exposed steel will still be protected by the remaining zinc.
- The zinc protects its base metal by corroding before iron. For better results, application of chromates over zinc is also seen as an industrial trend.
No other protective coating for steel or pipe provides the long life, durability and predictable performance of hot dip galvanising. An alloy of its steel base, a galvanised coating is unique in matching the design and handling characteristics of steel.
Galvanising is a once only process, committed to the concept of the maintenance-free use of steel, ensuring long service life and virtually eliminating disruptive maintenance.
Metallic zinc is strongly resistant to the corrosive action of normal environments and hot dip galvanised coatings therefore provide long-term protection for steel. By contrast, most organic paint coatings used on steel need frequent renewal and when coatings are breached.
Although galvanising will inhibit attack of the underlying steel, rusting will be inevitable after some decades of exposure to weather, especially if exposed to acidic conditions. For example, corrugated iron sheet roofing will start to degrade within a few years despite the protective action of the zinc coating.
Construction Steel & Pipe
This is the most common use for galvanised steel, and hundreds of thousands of tons of steel products are galvanised annually worldwide. Typically, these include street furniture, building frameworks, balconies, verandas, staircases, ladders, walkways, and more.