Which corrosion category is not readily removable and projects beyond the surface?

• A. Minor Corrosion
• B. Etching
• C. Developed Rust
• D. Major Corrosion

Answer: (D)

Understanding how corrosion progresses helps you judge what action is needed. When corrosion is described as not readily removable and it projects beyond the surface, you’re looking at a severe, advanced form. This means material loss has occurred and corrosion products have built up into a raised area above the surrounding surface, making normal cleaning ineffective and signaling that the component likely needs repair or replacement.

The other descriptions point to milder conditions. Minor corrosion is shallow and can be wiped away or cleaned off; etching produces a roughened surface from chemical attack without significant protruding features; developed rust indicates rust formation that has progressed but doesn’t necessarily create raised, hard-to-remove projections.