The 8 most common types of corrosion and countermeasures

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Corrosion is a natural degradation process that occurs in metal materials within an environment; it not only causes significant economic losses but can also lead to serious safety accidents. For industrial applications that rely on metal components such as fasteners, equipment, and structures, a thorough understanding of the types and mechanisms of corrosion is the first step toward effective protection. This article provides a comprehensive overview of the eight main types of corrosion to help you identify risks and make informed decisions. What is corrosion? Corrosion is a gradual degradation process caused by a chemical reaction between a metal and its surrounding environment. Essentially, this is an electrochemical process in which metal atoms lose electrons and get oxidized, forming more stable compounds (such as oxides and hydroxides). This process damages the strength, appearance, and integrity of the material, which can ultimately lead to catastrophic failure. The basic conditions for corrosion to occur include: Anode: the metal area where oxidation takes place (losing electrons). Cathode: The area where reduction reactions occur (electrons are gained). Electrolyte: A medium that provides a path for ionic conduction (such as water or salt solutions). Conductive path: The metal pathway that connects the anode and the cathode. Detailed explanation of the eight most common types of corrosion. Below are the eight most common and harmful types of corrosion in industrial environments, especially in fastener applications: 1. Uniform corrosion: Description: Corrosion occurs evenly across the entire metal surface, resulting in a uniform thinning of the material as a whole. Common environments: humid atmospheres, industrial environments, acid rain. Effect on fasteners: It causes bolts, screws, etc. to gradually thin out, resulting in a decrease in tensile strength and clamping force, eventually leading to fracture. 2. Pitting: Description: A highly localized form of corrosion that results in small, deep holes (pitting pits). Highly concealed; often spreads beneath the surface. Common environments: Chloride-rich environments, such as the ocean, coastal areas, and chemical plants. Effect on fasteners: Even very small erosion pits can become stress concentration points, causing the fasteners to break suddenly at loads far below the designed value. 3. Stress corrosion cracking Description: A brittle fracture that occurs under the combined effect of tensile stress and a specific corrosive environment. This is one of the most dangerous forms of corrosion. Common environments: Austenitic stainless steels in chloride environments, or high-strength alloys in specific media. Effect on fasteners: The fasteners themselves are under high tensile stress immediately after installation, making them highly susceptible to SCC, which can lead to catastrophic failure without any warning. 4. Crevice corrosion Description: Localized corrosion that occurs within narrow gaps, such as under gaskets, at the contact surface between nuts and workpieces, or beneath deposits. Common environments: Any environment with gaps and stagnant electrolytes, especially those containing chlorides. Impact on fasteners: The area below the bolt head and the thread engagement zones are prone to crevice corrosion; this corrosion is difficult to detect until the fastener fails. 5. Galvanic corrosion Description: When two metals with different potentials come into contact in an electrolyte, the metal with the more negative potential (the more reactive one) will corrode more rapidly. Common environments: marine environments or structures using different metal combinations. Effect on fasteners: If the fastener is not compatible with the material it is connected to (such as using steel bolts on aluminum structures), it can cause one of the materials to corrode rapidly. 6. Intergranular corrosion Description: Corrosion occurs along the grain boundaries of the metal, resulting in a significant loss of the material’s strength. Common environments: Chromium depletion in the grain boundaries of stainless steel usually results from improper heat treatment or welding. Effect on fasteners: The internal bonding strength of the material decreases, causing the fasteners to suffer from brittle fracture despite appearing intact. 7. Abrasive corrosion Description: The combined effect of mechanical wear and corrosion caused by slight vibrations or repeated relative movement between two contacting surfaces. Common environments: Mechanical joints and bearings subjected to vibration loads. Impact on fasteners: It causes thread wear, loss of preload, and the formation of corrosion products, thereby exacerbating damage. 8. Hydrogen embrittlement: Description: Hydrogen atoms penetrate into the metal, leading to a decrease in toughness and strength in high-strength materials, thereby causing brittle fracture. Common environments: electroplating, pickling, cathodic protection processes, or environments with sulfur-containing hydrocarbons. Impact on fasteners: It causes severe damage to high-strength bolts, potentially delaying their fracture under static loads. Why is corrosion resistance so important? Ignoring corrosion protection has three major consequences: economic costs – Global losses due to corrosion amount to trillions of dollars each year, including costs related to repairs, replacements, and downtime. Safety risks: The failure of critical structures such as bridges, buildings, pipelines, and aircraft can lead to loss of life and environmental disasters. Product contamination: In industries such as food and pharmaceuticals, corrosion products can contaminate products, posing a risk to consumers’ health. Summary and countermeasures: Recognizing corrosion is the first step in overcoming it. Each type of corrosion has its own unique causes and corresponding protection strategies. For example, to deal with pitting and crevice corrosion, materials with a high PREN value (pitting resistance equivalent) should be chosen, such as duplex stainless steels or high-nickel alloys. The key to avoiding galvanic corrosion lies in carefully selecting the metal materials that come into contact with each other. To prevent stress corrosion cracking, it is necessary to optimize the design to eliminate tensile stress and avoid sensitive material-environment combinations. When selecting fasteners and materials for your critical applications, be sure to take into account all potential corrosion risks they may face. Choosing the right materials is the most cost-effective way to ensure the long-term safe and reliable operation of equipment. In addition, regular inspections of the pipeline’s anti-corrosion coating are necessary.