No other protective coating for steel 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.
As asset management and life-cycle costing become even more essential, after fabrication galvanising provides the facility to design for a predictable, engineered result.
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.
This long-term protection is well documented world-wide in terms ahead of any other protective coating, and galvanising continues to find new applications in almost every field of engineering.
Properties of Galvanising
Hot dip galvanising protects steel from corrosion by providing a thick, tough, metallurgically bonded zinc envelope, which completely covers the steel surface and seals it from the corrosive action of its environment.
The galvanised coating provides outstanding abrasion resistance. Where there is damage or minor discontinuity in the sealing coat of zinc, protection of the steel is maintained by the cathodic action of the surrounding galvanised coating.
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 corrosion begins at the exposed area of steel, spreading rapidly beneath the coating film.
The Galvanised Coating
The galvanising process produces a durable, abrasion-resistant coating of metallic zinc and zinc-iron alloy layers bonded metallurgically to the steel base and completely covering the work piece. No other coating for steel matches galvanising’s unique combination of properties and advantages:
1. For most classes of steelwork, galvanising provides the lowest longterm cost. In many cases galvanising also provides lowest initial cost.
2. The galvanised coating becomes part of the steel surface it protects.
3. The unique metallurgical structure of the galvanised coating provides outstanding toughness and resistance to mechanical damage in transport, erection and service.
4. The galvanised coating is subject to corrosion at a predictably slow rate, between one-seventeenth and one eightieth that of steel, depending on the environment to which it is exposed.
5. Galvanising’s cathodic protection for steel ensures that small areas of the base steel, which may be exposed through severe impacts or abrasion, are protected from corrosion by the surrounding galvanised coating.
6. An inherent advantage of the process is that a standard minimum coating thickness is applied.
7. During galvanising the work is completely immersed in molten zinc and the entire surface is coated, inside and out, even recesses and returns which often cannot be coated using other processes. If required, just the external surfaces of vessels and containers can be coated simultaneously. See our advice section for more information.
8. Galvanised coatings are virtually ‘self-inspecting’ because the reaction between steel and molten zinc in the galvanising bath does not occur unless the steel surface is chemically clean. It is not possible to have a galvanised coating that is not properly bonded to the surface of the steel. Therefore a galvanised coating which appears sound and continuous is sound and continuous.
9. Galvanising is a highly versatile process. Items ranging from small fasteners and threaded components, up to massive structural members can be coated. See our advice section for more information.
10. The mechanical properties of commonly galvanised steels are not significantly affected by galvanising. See ‘Mechanical properties of galvanised steels’.
11. Galvanising provides outstanding corrosion performance in a wide range of environments. See ‘Performance in various environments’.
12. ‘Duplex’ coatings of galvanising-plus-paint are often the most economic solution to the problem of protecting steel in highly corrosive environments. Such systems provide a synergistic effect in which the life of the combined coatings exceeds the total life of the two coatings if they were used alone. See ‘Painting galvanised steel’.