Define pitting factor.

• A. The ratio of the deepest pit depth to the total surface area affected.
• B. The difference between the deepest pit depth and the average pit depth.
• C. The ratio of the deepest pit depth to the average pit depth.
• D. The ratio of the deepest pit depth to the average metal loss; higher values indicate more severe pitting.

Answer: (D)

Pitting factor measures how severe a pitting corrosion attack is by comparing the deepest pit to the overall material loss. It’s defined as the depth of the deepest pit divided by the average metal loss over the exposed surface. When corrosion is uniform, the deepest pit isn’t much deeper than the average loss, so the factor is about 1.0. If one pit becomes much deeper than the rest, the deepest pit depth grows relative to the average loss, and the factor increases. This directly quantifies how localized the damage is, which is why the ratio of deepest pit depth to average metal loss is the best way to describe pitting severity.