Galvanization

Galvanization (or galvanisation in British English) is the industrial process of applying a protective zinc coating to iron or steel to prevent rusting. As an essential method of corrosion control, galvanization underpins modern construction, manufacturing and infrastructure by extending the service life of ferrous materials. The technique is most widely associated with hot-dip galvanizing, although several variations exist to suit different engineering requirements.

Protective Action and Corrosion Behaviour

Zinc forms a defensive layer that shields the underlying iron or steel from corrosive agents such as moisture and atmospheric oxygen. When the coating remains intact, it acts as a barrier preventing rust formation. Even when the surface is damaged, zinc offers additional protection through sacrificial action: it corrodes preferentially to the underlying metal, thereby delaying or preventing iron oxidation.
Further resistance to corrosion may be achieved through secondary treatments such as chromate conversion coatings, which enhance passivation and improve long-term durability. The combined effect of these measures enables galvanized steel to endure for several decades, particularly when maintained with supplementary coatings or sacrificial anodes.

Historical Development and Terminology

The term “galvanization” derives from the work of the Italian scientist Luigi Galvani (1737–1798). Although Galvani’s experiments concerned bioelectricity rather than zinc coatings, the terminology became fashionable in nineteenth-century science and was applied metaphorically to describe processes that seemed to “animate” or activate materials.
The earliest known example of galvanized iron occurs in seventeenth-century Indian armour, identified through modern X-ray fluorescence analysis. Industrial galvanizing became viable in the nineteenth century, especially after Stanislas Sorel patented a zinc-based “galvanic paint” in 1837, marking an early precursor to the contemporary hot-dip process.
The term “galvanized” has since acquired a metaphorical usage, referring to actions or events that provoke sudden activity or enthusiasm in individuals or groups.

Methods of Galvanization

Galvanizing technologies differ in coating thickness, metallurgical bonding and suitability for specific applications.
Hot-dip galvanizingThis is the predominant method used in construction and industrial production. Steel components are immersed in a bath of molten zinc, producing a thick, durable coating composed of zinc–iron alloy layers topped with pure zinc. The result is robust protection suitable for demanding environments. With the exception of high-strength steels—where hydrogen embrittlement may occur—hot-dip galvanizing does not substantially affect mechanical strength.
ElectrogalvanizationUsed extensively in vehicle manufacturing and decorative applications, electrogalvanizing employs an electric current to deposit a thinner, more uniform zinc layer. This facilitates the application of paint or other surface finishes.
Thermal diffusion galvanizing (Sherardizing)In this solid-state process, zinc powder diffuses into iron or copper-based substrates at elevated temperatures. Sherardizing produces a tightly bonded, wear-resistant zinc–iron alloy layer without exposing components to molten zinc.

Corrosion and Service Life

Galvanized steel performs well in a wide range of environments but is susceptible to chemical pollutants. In non-saline atmospheres, corrosion is driven mainly by sulphur dioxide levels, which influence the rate at which zinc is consumed. With adequate maintenance, including repainting and the installation of sacrificial anodes, galvanized structures may last many decades.
The longevity of galvanized products also depends on the thickness of the zinc coating. For example, galvanized pipes are classified on a scale from G01 to G360, indicating different coating weights.

Applications in Construction and Infrastructure

Galvanized steel is ubiquitous in modern building and engineering practices. Large quantities of structural and fabricated components are galvanized annually. Common applications include:

• Building frameworks, balconies and staircases
• Ladders, walkways and guard rails
• Street lighting columns and road furniture
• Fencing, railings and outdoor fixtures

Hot-dip galvanized steel is also used in steel frame buildings, providing a durable and cost-effective material capable of resisting harsh external conditions.

Galvanized Piping and Water Supply Systems

In the early twentieth century, galvanized pipes replaced cast-iron pipes in domestic plumbing. Despite their initial popularity, galvanized pipes exhibit internal corrosion over time. Rust forms from the inside outward, creating deposits or “plaque” that constrict water flow, reduce pressure and produce impurities or metallic tastes in tap water.
The typical lifespan of galvanized plumbing is 40–50 years, though installation quality and coating thickness greatly influence longevity. As a result, many older buildings undergoing renovation require replacement of aging galvanized piping systems.

Industrial and Material Considerations

Galvanization interacts with related metallurgical processes such as annealing, which may be used to prepare or stabilise steel prior to coating. Design decisions often include balancing coating thickness, structural requirements and exposure conditions.
Galvanized steel remains central to industrial design due to its favourable combination of cost, durability and ease of fabrication. Its widespread use across construction, infrastructure and manufacturing highlights the enduring relevance of galvanization in protecting metals from corrosion and extending their operational life.