Corrosion is a serious issue in engineering that involves the gradual degradation of materials (particularly metals) as they react with their surrounding environment. This process not only compromises the structural integrity and longevity of infrastructure and machinery but also inflicts significant economic losses. According to the World Corrosion Organization, corrosion in its many forms costs the global economy about $2.2 trillion annually.

At the core of the process of corrosion is the concept of electrical resistance, a property that significantly influences the rate at which corrosion occurs. Engineers are leveraging the interplay between corrosion and electrical resistance to develop more effective strategies for managing corrosion. These strategies include material selection, protective coatings, cathodic protection and environmental control, all of which will be covered in this article.

Figure 1: Engineers are leveraging the interplay between corrosion and electrical resistance to develop more effective strategies for managing corrosion. Source: corlaffra/Adobe StockFigure 1: Engineers are leveraging the interplay between corrosion and electrical resistance to develop more effective strategies for managing corrosion. Source: corlaffra/Adobe Stock

The electrochemical nature of corrosion and the significance of the electrical resistance

Corrosion is fundamentally an electrochemical reaction that occurs when a metal is exposed to an environment which leads to its oxidation. This reaction involves the metal acting as an anode and losing its electrons to the cathode (the part of the metal that gains the electrons). This process occurs in the presence of electrolytes (typically water containing dissolved oxygen salts and acids), which facilitate the flow of electrons between the anodic and cathodic sites on the metal’s surface.

Electrical resistance is the measure of a material’s opposition to the flow of electric current. It dictates the ease with which electrons move through a material, thus affecting the electrochemical reactions essential to the corrosion process. For instance, high resistance between the anode and cathode will slow corrosion by limiting the electrochemical reactions and the ease of electron flow through the metal.

Engineers rely on this relationship between electrical resistance and corrosion to gain valuable insights into the current state and future progression of corrosion. For instance, techniques such as electrical resistance monitoring are used extensively in pipelines, storage tanks and offshore platforms to detect corrosion that could lead to leaks or structural failures.

[Learn more about corrosion monitoring on GlobalSpec]

Strategies for mitigating corrosion

Material selection and coatings

A simple way engineers mitigate corrosion is by designing components with materials that have high intrinsic resistance to electron flow. Materials such as stainless steel, aluminum alloys, titanium and copper-nickel alloys are known to be less prone to corrosion. However, in cases where it is absolutely necessary to use certain materials that are prone to corrosion, protective coatings are applied on the surface of these materials. These coatings increase the surface’s electrical resistance and act as barriers that limit destructive electrochemical reactions. Protective coatings used in the industry range from simple paints to advanced materials like epoxy, polyurethane and fluoropolymer coatings.

[Learn more about protective coatings on GlobalSpec]

Cathodic protection

Cathodic protection is a technique that operates by making the metal surface the cathode of an electrochemical cell. The process involves two primary methods:

  1. Sacrificial anode cathodic protection (SACP) method
  2. Impressed current cathodic protection (ICCP) method

In the SACP method, a more easily corroded metal (called the sacrificial anode) is electrically connected to the metal that needs protection (cathode). When these anodes and cathodes are placed in a corrosion-inducing environment like soil or water, the anode is preferentially corroded. This happens because the anode, having a higher electrochemical potential, donates electrons to the cathode. The electron flow neutralizes the reactive sites of the cathode where corrosion would occur. Common metals used as sacrificial anodes in the SACP method include zinc, magnesium and aluminum.

In contrast, the ICCP method uses an external power source to provide a constant electrical current to the metal that needs protection, making it a cathode. Anodes made of durable materials such as silicon and metal oxides, which do not corrode away like the sacrificial anodes are used. Engineers find this approach useful in applications featuring large metal structures or where the use of sacrificial anodes is impractical due to size and longevity considerations. Examples of application areas of the ICCP method include reinforced concrete structures, buried storage tanks and offshore oil platforms.

Environmental control

Engineers can also mitigate corrosion by controlling the environmental conditions that favor the corrosion reaction. For instance, measures such as reducing humidity, limiting exposure to harmful chemicals and applying water-repellant coatings can enhance the resistance at the interface between the metal and its environment.

Conclusion

Corrosion is a complex challenge that intersects with the fundamental properties of materials, notably their electrical resistance. By understanding how electrical resistance affects corrosion, engineers can better predict, monitor and mitigate this issue. While this article presents some of the basic strategies for mitigating corrosion, consulting with corrosion mitigation service providers is recommended to tailor approaches to unique requirements.

To contact the author of this article, email GlobalSpeceditors@globalspec.com