Hot-dip galvanizing (HDG), as referenced on this site, is the process of dipping fabricated steel into a kettle or vat of molten zinc. While the steel is in the kettle, the iron metallurgically reacts with the molten zinc to form a tightly-bonded alloy coating that provides superior corrosion protection to the steel.
The term “galvanizing” is often used incorrectly to describe various zinc coatings for steel. The hot-dip galvanizing process the AGA and its members produce is also commonly referred to batch, general, or after-fabrication hot-dip galvanizing and is not the same as in-line or continuous sheet galvanizing. Continuous sheet galvanizing, a coil-to-coil process used on 10-28 gauge sheet steel, is produced in a slightly different process. For more information about continuous sheet galvanizing and those products (G60, G90, etc.), please contact the GalvInfo Center at www.galvinfo.com.
In addition to hot-dip galvanizing and continuous sheet galvanizing, there are a number of other zinc coatings applied to steel such as zinc-rich paint, electro-statically applied (plated) zinc, metallizing, and mechanically applied zinc. All of these zinc coatings are significantly different than hot-dip galvanizing and may be inappropriate for many situation and environmental exposures.
History of Hot-Dip Galvanizing
Record of zinc usage in construction began in 79 AD, which could be considered the origination of galvanizing.
However, the first recorded history of galvanizing dates back to 1742 when P.J. Malouin, a French chemist, presented to the Royal Academy of Sciences several experiments involving coating iron with molten zinc.
In 1772, Luigi Galvani, galvanizing’s namesake, discovered the electrochemical process that takes place between metals during an experiment with frog legs.
Alessandro Volta furthered the research on galvanizing when he discovered the electropotential between two metals, creating a corrosion cell.
Michael Faraday discovered zinc’s sacrificial action during an experiment involving zinc, salt water, and nails.
Shortly after,French engineer Stanislaus Tranquille Modeste Sorel took out a patent for the early galvanizing process.
By 1850, the British galvanizing industry was consuming 10,000 tons of zinc annually for the production of galvanized steel.The United States, slightly behind, had its first galvanizing plant open in 1870. At the time, the steel was hand dipped in the zinc bath.
Today, more than 600,000 tons of zinc is consumed annually in North America to produce hot-dip galvanized steel. Galvanizing is found in almost every major application and industry where iron or steel is used. The utilities, chemical process, pulp and paper, automotive, and transportation industries, to name just a few, historically have made extensive use of galvanizing for corrosion control. They continue to do so today. For over 150 years, hot-dip galvanizing has had a proven history of commercial success as a method of corrosion protection in myriad applications worldwide.