Hot dip galvanizing (or hot dip coating) is a process developed to prevent steel from corroding. Before the process can take place, the steel goes through a thorough chemical clean which removes all rust, oil and mill scale from the surface. When the cleaning solution has been rinsed off, the coating process can begin. The steel is dipped into a bath of molten zinc heated to around 450°C (860°F) before being left to cool in a quench tank. When the cooling process is complete, the zinc coating is then metallurgically bonded to the steel. Hot dip zinc plating protects the underlying steel from exposure to corrosion from moisture, oxygen, and chemicals. It significantly extends the lifespan of the coated metal, even in the harshest environments.

The galvanizing process should not be viewed in isolation but must be considered at the design stage. Some parts may need extra venting or drainage points and, in the case of internal tread forms, a post-galvanizing operation will be necessary. If certain areas of the steel need to be left uncoated, these areas need to be properly masked before the galvanizing process. We offer free advice and guidance on best design practices to give you the best quality galvanizing.

1 – Long life

Galvanizing creates an easy-to-clean surface which can give a maintenance-free life of more than 70 years (depending on the environment it is being used in). When maintenance eventually becomes necessary, it is straightforward. No complex preparation treatments are necessary.

2 – Competitive initial cost

For many applications, the cost of hot dip galvanizing is lower than that of applying alternative coatings. The reason is simple: alternatives, particularly painting, are highly labour-intensive compared to galvanizing, which is a highly mechanised, closely controlled factory process.

3 – Lowest lifetime cost

Low initial cost and long life make galvanizing the most versatile and economic way of protecting steel for long periods. The benefits of no maintenance, or extended maintenance intervals, include fewer problems of access in remote areas, difficult terrain, when buildings are closely packed together or when there are safety restrictions such as electricity pylons.

4 – Reliability

The process is relatively simple, straightforward and closely controlled. The thicknesses (weights) of coatings formed are regular, predictable and simply specified. Hot dip galvanizing is defined by a single British Standard – EN ISO 1461.

5 – Speed of application

A full protection coating can be applied in hours; a complicated paint system can require a week.

6 – Coating toughness

Galvanizing is unique. The hot dip process produces a coating which is bonded metallurgically to the steel. No other coating process has this feature and, as a result, galvanized steel has by far the greatest resistance to mechanical damage during handling, storage, transport and construction – an important factor where steelwork is to be shipped around the world.

7 – Complete coverage

Because it is formed by dipping steel into molten zinc, all parts of the surface of the steel are coated – inside, outside, awkward corners and narrow gaps which would be impossible to protect in any other way. The coating actually tends to build up at vital corners and edges – rather than thinning out as is often the case with brushed, sprayed and other dipped coatings.

8 – Three-way protection

Galvanized coatings protect steel in three ways:-

• The coating weathers at a very slow rate, giving a long and predictable life.
• The coating corrodes preferentially to provide cathodic (sacrificial) protection to any small areas of steel exposed through drilling, cutting or accidental damage. Scratches are sealed by weathering products from the zinc.
• If the damaged area is larger, the sacrificial protection prevents the sideways creep of rust which can undermine paint coatings.

9 – Ease of inspection

Galvanized steel simplifies inspection of the protective finish. The nature of the process is such that if the coating looks continuous and sound, it is! Thicknesses – simply specified through EN ISO 1461 – can be easily checked with an electronic probe.

10 – Faster construction

Galvanized steel is ready for use. No further site surface preparation, painting, touch-up or inspection is necessary and cladding can begin immediately, thus accelerating construction time.