What type of corrosion damage appears as a gray, black or reddish film on ferrous metals and in various color formations on nonferrous metals (blue-green on copper, brass, and bronze and as a white powder on aluminum). It is readily removable and does not project beyond the surface?

• A. Major Corrosion
• B. Minor Corrosion
• C. Etching
• D. Pitting

Answer: (B)

This item tests recognizing corrosion that stays at the surface rather than causing deeper damage. The described films are typical surface oxides or patinas that form on metals: a gray, black, or reddish film on ferrous metals and blue-green colors on copper, brass, and bronze, plus a white powder on aluminum. These coatings can be wiped or washed away and do not stand out or protrude beyond the metal surface, which means the corrosion is superficial. That’s what makes it minor corrosion.

If it were major corrosion, you’d see substantial material loss or structural damage. Etching implies chemical attack that roughens the surface rather than just leaving a removable film, and pitting involves small holes that extend below the surface.