Which term describes corrosion that occurs at discrete sites on a metal surface?

• A. Localized corrosion
• B. Uniform corrosion
• C. Galvanic corrosion
• D. Intergranular corrosion

Answer: (A)

Localized corrosion happens when corrosion doesn’t spread evenly across the surface but concentrates at specific spots, creating pits or small areas of attack. This pattern arises when protective films break down locally, at defects, crevices, or where aggressive species like chloride ions are concentrated, so you end up with discrete sites of damage rather than uniform thinning. In contrast, uniform corrosion wears the entire exposed area more or less evenly, halving or thinning the metal surface uniformly. Galvanic corrosion requires two different metals in electrical contact within an electrolyte, driving accelerated attack on the more anodic metal at the contact points, which isn’t about discrete pits on a single surface. Intergranular corrosion runs along grain boundaries due to microstructural factors, which is a different kind of localized attack tied to the material’s structure. So the term that best describes corrosion at discrete sites is localized corrosion.