Which corrosion mode is deep and narrow and may rapidly penetrate the material?

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

Answer: (A)

Pitting is a localized, deep and narrow corrosion attack that can rapidly penetrate the metal. It starts when the protective film on the surface breaks down at a small spot, often due to chloride ions or impurities. Once a pit forms, it tends to grow downward because the pit environment becomes highly aggressive—oxygen is depleted and metal ions accumulate, speeding dissolution inside the pit even though the surrounding surface looks largely intact. This combination allows a tiny pit to penetrate deeply with relatively little overall surface corrosion, making it easy to miss until thinning or failure occurs. Uniform corrosion spreads evenly across the surface, and broader localized corrosion is not necessarily as deep or focused as a pit.