Which of the following is NOT a type of localized corrosion?

• A. Hydrogen-induced cracking
• B. Pitting
• C. Crevice
• D. Filiform

Answer: (A)

Localized corrosion refers to attack that is confined to small, specific areas on the metal surface, producing features such as pits, crevices, or coating-related patterns. Hydrogen-induced cracking, however, is a cracking mechanism caused by hydrogen entering the metal, diffusing through the lattice, and embrittling the material, which leads to cracks rather than distinct surface pits or crevice-like attacks. It’s driven by hydrogen effects in the bulk material and is typically categorized as environmentally assisted cracking, not a surface-localized attack. The other forms—pitting, crevice corrosion, and filiform corrosion—are classic examples of localized attack, each confined to a region and producing characteristic surface features. Hence, hydrogen-induced cracking is not a type of localized corrosion.