Galvanized steel plays a critical role in infrastructure in the quarrying industry. This ranges from steel shaft structures to stope structures (roof supports, pipe hangers), haulway structures (aggregate transfer stations, electrical stubbies) as well as surface structures (plant buildings, tank supports, pipe gantries, conveyor belts, stacks, stockpile structures, stairways, railings).
The environmental conditions in the quarrying industry can often be aggressive and the service demands on steel extreme, subjecting it to maximum demands. These conditions include water immersion, impact and abrasive conditions, extended surface wetness, variable temperatures, and corrosive underground atmospheres.
Hot dip galvanized coatings have a good track record in protecting many structural steel parts in surface mining environments.
South Africa’s quarries have ever present corrosive water, which is where hot dip galvanized (duplex coated) steel really comes into its own. Thus, a cost-efficient, long-lasting, and maintenance-free protection system for steel should be specified, which means a duplex coated galvanized steel system, explains Simon Norton, Executive Director of the International Zinc Association (IZA) Africa.
Galvanizing provides a tough and abrasion-resistant coating as well as long-term corrosion protection of steel in two ways: As a physical barrier to corrosive atmospheres, and by means of galvanic or sacrificial protection, which is unique to zinc, significantly extending the service life of steel in even the most challenging environments.
Surface
Atmospheric environments are classified into different categories of severity by ISO 9223, which also provides a range of lifetimes for steel and zinc in these environments. There is a specific relationship between galvanized zinc coating thickness and expected coating life, defined as the time that can pass before coating maintenance is required to restore protection to the base metal.
Added corrosion protection: The duplex system
Organic (paint) coatings can be added for improved corrosion protection. If hot dip galvanized steel is then overcoated with a tough organic paint system, the resultant duplex coating has an extended lifetime, saving the mine owner money.
On the other hand, continuous galvanized sheet is generally pre-painted in the same facility in which a thin zinc galvanized coating is applied. This allows for precise preparation of the galvanized surface prior to coil coating. Painted galvanized sheet can be roll-formed to give profiles as specified by the customer for roofing and cladding of surface plant.
Combining paint coatings with galvanized coatings is referred to as a duplex system. Duplex systems benefit from a synergistic effect that enables the combined life of the painted galvanized steel to be longer than the sum of the individual lives of the paint and galvanized coatings in the same environment. The synergy multiplier ranges from 1,8 to 2,7, depending on the severity of the corrosion conditions.
Hot dip galvanizing provides superior corrosion protection to steel. It is easily and swiftly applied and covers the entire surface of the steel article, even in inaccessible areas, provided the component is designed properly. Hot dip galvanized coatings offer a unique dual protection that prevents corrosion even if the coating is damaged.
Maintenance painting is often impossible in mining environments, meaning the only option with paint-only structures is complete replacement. Hot dip galvanized coatings, however, are hard and abrasion resistant. They provide long lasting and maintenance-free corrosion protection to steel even in aggressive mine environments, and provide significant savings compared with other protection systems that require maintenance.
REFERENCE
https://www.zinc.org/wp-content/uploads/sites/4/2015/01/Hot-Dip-Galv-in-Mining-Brochure-36pp.pdf.
