After the era of stone tools, humans began to use metals because of their unique properties. Metals such as copper, iron, silver, and later aluminum and zinc were widely used in various industries. However, the major problem with these materials was their instability in pure form and their tendency to convert into compounds such as metal oxides, which would destroy the metal. It was at this time that the need for a science called corrosion science [1] and the study of the causes of this unwanted phenomenon and methods of preventing it was considered. Corrosion of metals occurs in various forms and for various reasons, but the most important reason for its occurrence can be examined in electrochemical reactions in metals.
According to research conducted in the United States between 1999 and 2000, direct losses due to corrosion were estimated at around $276 billion per year. The magnitude of this figure becomes clear when this number is compared to the US gross national product. Accordingly, this cost is equivalent to 3.1% of the total US gross national product, of which $137.9 billion is allocated to the industrial sector alone. Informal studies were also conducted in Iran on this subject. According to this research, direct losses due to corrosion were estimated at around 5000 billion rials in 1994, around 9000 billion rials in 1997, and around 27500 billion rials in 1999.
Specifically, if we examine corrosion in iron and steel, we will find that the two factors of moisture and the presence of oxygen create an electrochemical cell on the surface of the metal, which over time oxidizes the metal and causes it to rust.
By eliminating any of the factors that cause corrosion, this process can be delayed, although it is almost impossible to completely prevent this phenomenon. Some methods of preventing corrosion are listed below:
Surface coatings
Anti-corrosion coatings are the most widely used and cheapest method for protecting metals. These coatings prevent the penetration of air, moisture, and generally external destructive factors into the coating by creating a resistant barrier. The mechanisms and methods used in these coatings for corrosion protection are examined in detail in the article Anti-corrosion Coatings.
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Cathodic protection
In this method, the structure is protected by placing an active metal (such as zinc) next to the body of a less active metal (such as steel). This method is widely used in the protection of gas and oil pipelines, buried structures and marine vessels. Also, in some cases, a direct current of electricity is also used alongside this system. This electric current tries to reverse the electrochemical process of corrosion. This method is widely used in oil and gas pipelines.
Zinc ingots placed on an oil platform to prevent corrosion of the platform base and body
Zinc ingots stacked next to oil pipelines
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