Chapter 3: Eight Forms of Corrosion: Mechanisms & Prevention

Eight Forms of Corrosion: Mechanisms & Prevention begins with uniform attack, the most common and predictable type of corrosion where the chemical reaction proceeds evenly across the entire exposed surface, resulting in measurable metal thinning. The text then explores galvanic corrosion, which occurs when two dissimilar metals are electrically coupled in an electrolyte, causing the more active metal to corrode faster while protecting the more noble one. This section emphasizes the importance of the galvanic series and the area effect, where a small anode coupled to a large cathode results in rapid failure. Crevice corrosion is detailed as an intensive localized attack occurring in shielded areas such as gaskets, lap joints, and under surface deposits where stagnant solutions lead to oxygen depletion and the accumulation of aggressive ions like chlorides. A related phenomenon, filiform corrosion, is described as a specialized type of crevice attack that occurs under thin protective coatings. Pitting is identified as one of the most destructive and insidious forms of corrosion, characterized by deep, localized holes that are difficult to detect and often result from autocatalytic processes that accelerate damage over time. The chapter further discusses intergranular corrosion, which targets grain boundaries due to alloy depletion or impurities, specifically highlighting weld decay and knife-line attack in stainless steels. Selective leaching is explained as the removal of one specific element from an alloy, such as the dezincification of brass or the graphitization of cast iron, which leaves behind a porous and weakened structure. Erosion corrosion focuses on the synergy between chemical attack and high-velocity fluid movement, including specialized failures like impingement and cavitation. Finally, the text addresses stress corrosion cracking, a brittle-like failure resulting from the combined influence of tensile stress and a specific corrosive environment, and concludes with an analysis of hydrogen damage, covering the mechanical degradation caused by hydrogen absorption, such as hydrogen blistering and embrittlement.