Hot-dip Galvanization: Best Solution Against Rusting and Corrosion

 Hot-dip galvanization has been extensively used to prevent corrosion for 100 years. Hot-dip galvanized steel has a great lifespan. This effective form of galvanization provides 2 levels of protection :

– Barrier protection

– Cathodic protection

 

In Cathodic protection, Zinc protects the underlying material. If any part is scratched, Zinc will prolong its protection. Zinc can also function as a barrier slowing down the corrosion rate.

 

What is Hot Dip Galvanizing?

Hot dip galvanizing 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.

 

There are three fundamental steps in the hot-dip galvanizing process, surface preparation, galvanizing, and inspection.

 

l Surface Preparation

When the fabricated steel arrives at the galvanizing facility, it is hung by wire or placed in a racking system which can be lifted and moved through the process by overhead cranes. The steel then goes through a series of three cleaning steps; degreasing, pickling, and fluxing. Degreasing removes dirt, oil, and organic residues, while the acidic pickling bath will remove mill scale and iron oxide. The final surface preparation step, fluxing, will remove any remaining oxides and coat the steel with a protective layer to prevent any further oxide formation prior to galvanizing. Proper surface preparation is critical, as zinc will not react with unclean steel.

 

l Galvanizing

After surface preparation, the steel is dipped in the molten (830 F) bath of at least 98% zinc. The steel is lowered into the kettle at an angle that allows air to escape from tubular shapes or other pockets, and the zinc to flow into, over, and through the entire piece. While immersed in the kettle, the iron in the steel metallurgically reacts with the zinc to form a series of zinc-iron intermetallic layers and an outer layer of pure zinc.

 

l Inspection

The final step is an inspection of the coating. A very accurate determination of the quality of the coating can be achieved by a visual inspection, as zinc does not react with unclean steel, which would leave an uncoated area on the part. Additionally, a magnetic thickness gauge can be used to verify the coating thickness complies with specification requirements.

 

Ten Good Reasons For Hot Dip Galvanizing

1 - Long life

Galvanizing creates an easy-to-clean surface that 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 labor-intensive compared to galvanizing, which is a highly mechanized, 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 that 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 when 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.

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8 - Three-way protection

Galvanized coatings protect steel in three ways:-

 

The coating weathers at a very slow rate, giving 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 the 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.

 

Hot Dip Galvanizing Plant Solutions - Hebei Annuo

Hebei Annuo is a global provider of Hot Dip Galvanizing Plant and Solutions, Specialty General HDG plant design and manufacture service. Hebei Annuo was founded in 1998, with more than 20 years experience in Galvanizing field, has built more than 30 complete Hot dip galvanizing plants in China and abroad. We have got ISO9001 and CE Certificates. Our products have been favored by more and more clients with the professional design, excellent quality and considerate service.

 

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