Corrosion
Corrosion is the process of deterioration of materials, typically metals, due to environmental factors such as moisture and oxygen. While often associated with rust, which is the visible damage resulting from corrosion, it is important to recognize that corrosion is the underlying mechanism that leads to such damage. Beyond metals, corrosion can impact a variety of materials, including polymers and ceramics, and is classified into various types based on where and how the damage occurs. The International Union of Pure and Applied Chemistry (IUPAC) defines corrosion as an irreversible reaction between a material and its environment, often resulting in loss of integrity and functionality.
The economic impact of corrosion is significant, costing around $3 trillion globally each year and causing serious safety risks, evidenced by numerous industrial accidents and infrastructure failures. Corrosion can manifest through several specific forms, such as uniform, localized, and intergranular corrosion, each affecting materials differently. Prevention techniques are crucial and can include environmental modifications, the use of corrosion-resistant materials, and protective coatings. By understanding and managing corrosion, industries aim to mitigate its effects and enhance material longevity.
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Subject Terms
Corrosion
Corrosion is a process marked by the deterioration of a solid material's physical integrity as the result of environmental conditions. One of its most familiar manifestations affects metal, which can oxidize when exposed to water or high levels of moisture in the air. This oxidization is widely known as rust, and it can be used to illustrate one of the most widely misunderstood aspects of corrosion. It is common for the terms rust and corrosion to be used interchangeably, but this is technically inaccurate. Specific to metal, corrosion refers to the progressive process of moisture-triggered deterioration, while rust is the result of that process. Thus, rust is more accurately described as corrosion damage.
While corrosion is most frequently associated with metal, the process can affect a wide range of different materials, including polymers, ceramics, and composite products composed of multiple base materials with differing physical properties. There are also many different types of corrosion, which are generally classified according to where the corrosion damage is localized on a given piece of material or by the root cause of the damage.
Background
Much of the scientific literature about corrosion focuses on its effects on metal, but the International Union of Pure and Applied Chemistry (IUPAC) has forwarded a more inclusive technical definition that has been widely adopted by scientific agencies around the world. The IUPAC definition is as follows: "Corrosion is an irreversible interfacial reaction of a material (metal, polymer, ceramic) with its environment which results in consumption of the material or in dissolution into the material of a component of the environment. Often, but not necessarily, corrosion results in effects detrimental to the usage of the material considered. Exclusively physical or mechanical processes such as melting or evaporation, abrasion, or mechanical fracture are not included in the term corrosion." Put more simply, corrosion is caused by a variety of damaging environmental agents and can affect a wide range of metal, polymer, and ceramic materials. It cannot be reversed, and in some cases, corrosion damage may result in the affected material being partially or entirely absorbed by the triggering material in the external environment.
As the IUPAC definition notes, corrosion can compromise the functional integrity of the affected material, and for this reason, industrial engineering efforts prioritize corrosion prevention as a primary objective. According to the Financial Times in 2022, corrosion costs the global economy about $3 trillion each year in damage to steel buildings and infrastructure.
Beyond the economic costs, corrosion can also pose serious risks to human health and safety. Corrosion-related failure has been cited as a primary or secondary cause of many bridge collapses, industrial accidents, and oil and gas pipeline explosions. Prominent examples include an El Paso, Texas, pipeline explosion that killed twelve people in the summer of 2000 and a dangerous tank leak detected in 2013 at a nuclear power plant in Fukushima, Japan. Because of corrosion, a ride at the Ohio State Fair in 2017 collapsed, killing one person and injuring seven others.
Overview
In metals, corrosion results from prolonged exposure to a combination of moisture, oxygen, and other environmental irritants. Beyond these variables, metal also corrodes because of surface processes marked by electrochemical changes that accelerate the development of corrosion damage. One such electrochemical process is known as galvanic action, which occurs when two different metals, positioned in prolonged, close contact with one another, generate low levels of electrical current, causing the continuous erosion of the structure's physical integrity. Galvanic corrosion can also occur in crevices and cracks that form in a metal material's surface. Corrosion cost the United States about $449 billion in 2023, according to an industrial services company. The economic impact of this much money on the country was about the same as the loss of a large company such as Walmart or Meta.
There are many other specific subtypes of corrosion, including uniform, localized, selective, wide-pitting, intergranular, transgranular, exfoliation, and interfacial corrosion. Uniform corrosion is defined as a corrosive chemical reaction that begins on a material's surface and extends across that surface in an even (uniform) manner. Localized corrosion, by contrast, affects only the base layers or the material, or certain isolated areas on the material's surface. Selective corrosion is similar to localized corrosion, except that it affects only certain specific structural components of a given material. Wide-pitting corrosion damage features broad pits, informally known as scars, which form on a material's surface. Intergranular and transgranular corrosion are rare types of corrosion damage, in that they affect the interior layers of a material rather than its surface. Exfoliation corrosion is a type of damage that results in the differing layers of a material becoming physically separated, and it usually affects irregular or misshapen objects. Finally, interfacial corrosion is a form of corrosion damage that occurs in marine environments, at the point where the water meets the air.
While corrosion is irreversible, its progress can be slowed or even stopped altogether with the proper techniques. In industrial environments, corrosion prevention and management typically take one or more of six main forms, including modifications to the environment, the selection of materials with inherent corrosion resistance properties, electrochemical protection, and the application of corrosion inhibitors and/or coating and plating compounds that protect the material from the damaging effects of moisture, oxygen, and harsh chemicals. Key prevention principles include removing the material from the corrosive environment, or altering the environment to be less corrosive. For example, storing a metal drum outdoors will make it more prone to corrosion from rain exposure. Moving the metal drum indoors, where it will remain dry, can prevent it from developing rust and other forms of corrosion damage. Similarly, hard water contains alkaline agents that can corrode metal. Adding softening agents to the water will make it less corrosive, thus reducing the likelihood of the immersed metal suffering corrosion damage.
Protective coatings, such as urethane, acrylic, and epoxy polymer coatings, can be applied to metal surfaces to increase their ability to resist corrosive agents. This strategy is commonly used in industrial material handling applications, such as oil and gas pipelines or storage drums. A technique known as plating, which involves the application of a metallic coating, can also be used to similar ends.
Bibliography
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