Which form of corrosion is an advanced form of intergranular corrosion?

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

Answer: (C)

Exfoliation corrosion is the progression of grain-boundary attack into a peeling, layered failure. Intergranular corrosion occurs when the metal along grain boundaries becomes anodic and deteriorates faster than the surrounding grains. When this attack becomes extensive, corrosion products build up between the grains and create enough pressure to lift and separate layers of metal, causing the surface to flake off in sheets. That layered peeling is what distinguishes exfoliation from ordinary intergranular attack, so it’s considered an advanced form of it. Uniform surface corrosion thins the metal evenly, pitting makes isolated holes, and plain intergranular corrosion is confined to the boundaries without the peeling layers.