Pitting corrosion is characterized by corrosive attack in a localized region surrounded by corrosion-free surfaces, or surfaces that are attacked to a much lesser extent.

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

Answer: (A)

Pitting corrosion is a localized form of attack where corrosion concentrates in tiny pits, while the surrounding surface remains relatively corrosion-free or only lightly attacked. This description exactly matches the scenario of a small, deep pit forming in a metal with the rest of the surface looking intact. It often occurs when a protective film on the metal surface breaks down in a localized spot—such as stainless steels or aluminum in chloride environments—allowing a pit to start and continue growing beneath the surface, sometimes going unnoticed until it becomes critical.

Other options don’t fit as well because they describe different patterns of attack. Localized corrosion is a broader term that includes pits but isn’t specific to the tiny, deep, isolated holes described here. Uniform corrosion implies a steady, even loss of material across a large area, not concentrated pits. Galvanic corrosion results from a potential difference between two different metals in contact, causing preferential attack on one metal and not the characteristic isolated pits with surrounding untouched areas.