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What is corrosion?

When metal is in contact with moisture an electrochemical reaction occurs leading to metal loss, we call it rust. This damage creates potential health and safety issues as well as expensive repair and/or replacements costs. Corrosion costs approximately 2.5 trillion dollars, or more than 3% of the global Gross Domestic Product. But corrosion control practices can limit damage – saving 375 to 875 billion dollars a year. How is corrosion identified and addressed? The science of corrosion prevention and control is highly complex, because corrosion can be caused by many factors, and it takes many different forms. What causes corrosion? Environmental factors can quickly deteriorate materials, especially metals. Exposure to salt water, humidity, and soil resistivity are three common factors that can increase the likelihood of corrosion formation. How is corrosion formed? Corrosion begins in the electrochemical cell. While there are some rare forms of high-temperature corrosion, the majority of corrosion occurs when specific environmental, electrical or chemical mechanisms cause the anode in the cell to corrode while the cathode does not. The resulting electrolytic paths and ionic current flows create a potential difference that drives corrosion. The elements that are common to all corrosion cells are: • an anode where oxidation and metal loss occur, • a cathode where reduction and protective effects occur, • metallic and electrolytic paths between the anode and cathode through which electronic and ionic current flows, and • a potential difference that drives the cell. Corrosion can be identified in one of three ways: • Visual examination • Supplementary examination, or testing • Verification by microscopy Once corrosion is identified, it can be classified as “general corrosion” which is more or less uniform over an exposed surface, or “localized corrosion” which occurs at discrete sites. There is also microbiologically influenced corrosion, or MIC, which occurs in the presence of fungi, bacteria, microalgae, and other microbiologically active materials like sewage. Identifying corrosion is the first step in preventing and mitigating damage. In the next videos, learn more about the forms of corrosion and how you can help control the process. Visit www.ampp.org to learn more.