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It&#;s estimated that up to 4% of the world&#;s GDP is lost through corrosion each year. When installing a steel fence, rust prevention should always be a key consideration; the materials and methods used will have a major impact on the longevity of your fence.
One of the best ways of protecting against corrosion is hot-dip galvanisation: a process in which the entire fence surface is dipped into molten zinc, coating it completely. This provides a barrier protection between the metal and its surrounding environment.
Without protection, steel will rust over time due to atmospheric conditions, with the degree of corrosion depending on the environment that the product is in. Steel is made mainly from iron and the rust is an iron oxide (typically a red oxide) which is formed by the reduction and oxidation reaction of iron and oxygen, in the presence of moisture.
Galvanisation is highly effective in preserving your fence because the corrosion of zinc, which protects the base metal, is very slow. A deep scratch in the surface of the zinc will expose the underlying metal; a galvanic cell is formed at this location, around which the zinc corrodes but still protects the metal &#; a process known as cathodic protection. The zinc acts as an anode and provides free electrons, sacrificing its ions and keeping the less active metal underneath from rusting. A zinc coating therefore provides &#;sacrificial protection&#;.
Other protective methods include painting or plastic coating, but these have serious flaws if used as the only method of protection and being applied directly to the steel substrate. When damaged, these inferior coatings can fall away, making them unreliable and in need of constant maintenance.
The galvanising process has a number of stages, all by immersion, that are required to achieve the final finish:
Acid or alkaline-based proprietary products may be used and they may be heated or used at ambient temperatures.
This is done in dilute hydrochloric acid which dissolves rust and produces a chemically clean surface.
A mixture of zinc chloride and ammonium chloride in solution is the standard agent of choice. The steelwork must be dry on completion of this stage.
The final stage involves the clean metal being immersed in a special bath of molten zinc at 450°C where the zinc alloys with the iron in the steel to form zinc/iron alloy layers. These layers are the basis of the coating.
At Jacksons Fencing, polyester powder coating can be applied if required after galvanising to protect the steel from rusting which allows the steel to not peel off with the paint still stuck to it. For installations near coastal areas, a marine coating can ensure that moisture does not get through to the galvanising below, helping to protect the finished product.
Being a well-established process that&#;s helped combat steel corrosion for over a century, the benefits of galvanisation have been proven extensively. The main benefits are as follows:
Even in cases where the initial cost of galvanising is higher than alternative coatings, galvanising is always cheapest in the long term because it lasts longer and doesn&#;t require constant care.
Galvanising offers complete coverage, sealing the base metal and stopping corrosion for good, eliminating the need for continual maintenance. The long-term durability is achieved at relatively low environmental burden.
Galvanising provides maximum protection through a tough, abrasion-resistant coating of increased thickness.
The lifespan of a zinc coating is largely determined by its thickness.
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If rust is a concern either use a metal that doesn&#;t corrode, or coat one that does. Metals that don&#;t rust &#; looking at you, stainless steel &#; carry a cost penalty, and often a performance one too. Coating lets you use a metal that&#;s less expensive and often easier to work. Paint is the first coating that comes to mind when looking to protect mild steel, but it doesn&#;t last very long. So that leads us to galvanizing, and the million-dollar question: Does galvanized steel rust?
The short answer is, yes, and also no. Galvanization is a zinc coating applied over the top of steel. It prevents rust and corrosion far longer than paint will, often for 50 years or more, but eventually that brown rot will set in. Want to know why? Keep reading to find out.
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Let&#;s start with some definitions. Corrosion is how metal breaks down as oxygen attacks the surface. Rust is the special type of corrosion experienced by iron. Oxygen creates iron oxide, which flakes away from the body of the metal, exposing fresh metal to oxygen.
Metals that don&#;t rust, like aluminum and stainless, form an oxide layer on the surface. This resists further corrosion. Another metal that oxidizes without rusting is zinc, and zinc is interesting because it bonds well to steel.
So, if you want to give steel a coating that lasts longer than paint, cover it with a layer of zinc. And that&#;s galvanization.
Zinc prevents oxygen and water from reaching the steel beneath. It does this by first forming a zinc oxide layer on the surface. When there&#;s moisture present that turns into zinc carbonate. This gives the metal a dull gray patina that&#;s insoluble in water and stops any further chemical changes.
So why doesn&#;t galvanized steel last forever? Keep reading.
Having said that zinc carbonate is insoluble, that&#;s not completely true. It will break down slowly under certain conditions. These include:
Relative humidity above 60%. (Tropical environments, hothouses used for raising tropical plants)
Sodium chloride (salt) in water or air. (Marine or coastal environments.)
Situations where the coating is frequently wet or soaked. (A car wash would be an example.)
Sulfur dioxide pollution in urban atmospheres.
Exposure to hydrogen sulfide from volcanoes, hot springs, natural gas, and sewer gas.
Strong alkalis such as plaster and cement, (especially Portland cement,) as these contain chlorides and sulfates.
Acid rainwater runoff from roofs with wood shingles
Moss and lichen, which will hold moisture and create a high humidity micro-climate.
When you&#;re thinking about using galvanized steel it is important to consider what the local conditions will be like. More specifically, think about:
Air. High or low humidity, exposure to salt, acids or industrial pollutants. (Desert air: not a problem. Tropical city: potential problem.)
Soil. Burying galvanized steel in soil, (as the base of a fence post for example,) will expose it to more moisture. However, the size of the impact depends very much on the type of soil and overall conditions, (muddy and wet or sandy and dry.)
Temperature. High temperature alone won&#;t break down zinc, providing it&#;s below the melting point of 787°F (420°C). It is however an accelerating factor when combined with corrosive factors like humidity and industrial pollution. Low temperatures have no effect on a galvanized coating.
So does galvanized steel rust? The answer is yes, but very slowly. In fact, slow enough that it&#;s usually not a problem. This is why galvanized steel has been in use for the last 2,000 years, and why it&#;s probably going to be okay in your application.
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