Steel is an ecofriendly construction material as it is durable and renewable, however, there is a need to extend the service life of the steel, which hot dip galvanising is well suited for, says Hot Dip Galvanisers Association Southern Africa (HDGASA).
Hot dip galvanising offers benefits, including reduced initial capital cost, durability, predictable performance, resistance to abrasion and low maintenance.
“Together with the ease of inspection of an ‘honest-coating’, hot dip galvanising has historically proven itself as effective and universally appropriate as an ideal corrosion control technology for iron and steel for nearly 150 years,” says HDGASA marketing manager Anthony Botha.
Hot dip galvanising is a metallurgical reaction between a perfectly clean iron or steel substrate submerged into a bath of molten zinc, resulting in the development of the zinc and zinc-iron alloy coating at the surface of ferrous metals. A hot dip galvanised coating acts both as a physical barrier while also working as a sacrificial anode.
When zinc reacts with atmospheric oxygen, zinc oxide is produced and also forms zinc hydroxide in the presence of moisture. The zinc hydroxide further reacts with carbon dioxide in the atmospheric environment, to produce a thin layer of impermeable zinc carbonate, which binds to the zinc beneath. This zinc carbonate ‘patina’ protects the zinc layer from any further corrosive oxidation of metallic components.
Further, there are numerous advantages to hot dip galvanising steel. A ton of coated zinc saves between 20 t and 30 t of steel from corrosive destruction over the period of the zinc’s service life. The galvanising process provides not only a low initial cost, but also one of the lowest life cycle costs among all of the protective coating techniques.
A hot dip galvanised coating develops from a metallurgical reaction between the steel and molten zinc, providing superior adhesion characteristics; it is a surface that can withstand ultraviolet radiation without suffering any damage and is highly resistant to damage through abrasion.
Moreover, hot dip galvanising coating when used in combination with an additional barrier coating provides synergistic corrosion control benefits well beyond that of individual corrosion control systems – this is known as Duplex Systems.
By-products of the hot dip galvanising process can be recycled and reused or repurposed.
“Steel and hot dip galvanising provide the engineering and construction sectors with the most effective means of delivering value to the end-user and society in general,” Botha concludes.