Crevice corrosion occurs where there is localized depletion of oxygen. Where is this most likely to occur?

• A. On raised surfaces
• B. Uniform on all exposed surfaces
• C. In high-temperature environments
• D. Under crevices or occluded areas

Answer: (D)

Crevice corrosion is driven by differential aeration: in a tight crevice, diffusion of oxygen to the metal surface is restricted, so oxygen becomes locally depleted inside the crevice. The surrounding exposed surface has more oxygen and remains relatively cathodic, while the crevice interior becomes anodic and dissolves, concentrating corrosion at the crevice base. That’s why the most likely location is under crevices or occluded areas such as joints, gaskets, fastener interfaces, or any hidden, stagnant gaps. The other scenarios don’t create the same localized oxygen depletion: raised surfaces get plenty of oxygen, uniform exposure would require uniform diffusion, and simply high temperature isn’t the defining cause of crevice-type localization.