Which term describes corrosion that occurs at a localized region surrounded by relatively corrosion-free areas?

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

Answer: (A)

Pitting corrosion describes corrosion that starts at a tiny, localized spot and forms a deep cavity while the surrounding metal remains comparatively clean and intact. This happens when a protective oxide or passive film on the metal surface breaks down at a small area—often due to chlorides or other aggressive ions—allowing metal to dissolve vigorously at that spot. Because the rest of the surface stays relatively protected, the overall metal loss can look minimal even though a pit can penetrate deeply. This is different from uniform corrosion, which progresses evenly over the entire surface, and from galvanic corrosion, which involves accelerated attack on one metal in a pair due to electrical contact with a more noble metal. It’s also more specific than the broad term localized corrosion, which encompasses any corrosion confined to a small area; pitting is the classic term for a localized, pit-like attack. In short, the description matches pitting corrosion.