Why is pitting corrosion more difficult to define than general corrosion?

• A. Because pits occur uniformly across the metal surface.
• B. Because pits are always visible from the surface.
• C. Because pits form only in non-metal environments.
• D. Because the exact location of the pits cannot be predicted.

Answer: (D)

Pitting corrosion is a highly localized attack that starts at microscopic flaws and depends on very local chemistry, so it doesn’t spread uniformly across the surface. General corrosion, on the other hand, wears away material more or less evenly, making it easier to describe with a single, overall rate of metal loss. Because pits begin at discrete initiation sites and grow inward from those points, their exact locations on a component are unpredictable. That inherent unpredictability is what makes defining and characterizing pitting more difficult than general corrosion. In practice, engineers describe pitting by measurements such as maximum pit depth and pit distribution, rather than a uniform thinning rate, while general corrosion is described by an overall thickness loss or average rate. Pits can also be hidden beneath deposits or form at irregular times, further complicating pinpointing their locations.