Differential aeration corrosion is promoted in which condition?

• A. Low or stagnant flow causing oxygen concentration cells leading to localized corrosion
• B. High flow causing uniform corrosion
• C. Vacuum conditions
• D. High temperature only

Answer: (A)

Differential aeration corrosion occurs when there is a difference in oxygen available at different spots on the metal surface. In areas with low or stagnant flow, oxygen near the surface is consumed by the metal more quickly than it can be replenished, creating an oxygen gradient. Regions with more oxygen become cathodic and the depleted regions become anodic, driving localized attack (pitting or crevice corrosion). If flow is high, oxygen delivery is more uniform, reducing the gradient and favoring uniform, not localized, corrosion. Vacuum removes oxygen entirely, so this differential cannot develop, and high temperature alone speeds reactions but doesn’t create the necessary oxygen gradient. So, low or stagnant flow is the condition that promotes differential aeration corrosion.