Which form of corrosion is a common and severe problem, causing localized pits?

• A. Pitting
• B. Uniform Surface Corrosion
• C. Exfoliation Corrosion
• D. Intergranular Corrosion

Answer: (A)

Pitting corrosion is a localized form of attack where tiny initiation points on the metal surface become deep, narrow holes. It usually starts at defects, inclusions, or breakdowns in the protective oxide film, and it’s driven by aggressive ions such as chlorides found in marine or salty environments. Once a pit forms, it can grow downward quickly with little surface change, so significant material loss and possible structural compromise can occur while the surface still looks relatively intact. This combination of easy initiation and deep penetration makes it a common and severe problem, especially for stainless steels and aluminum alloys exposed to saltwater. Other forms attack the surface more uniformly or along layers or grain boundaries, so they don’t produce the characteristic localized pits described here.