Under-Deposit Corrosion

Definition

Under-deposit corrosion occurs when a foreign material covers the metal surface, creating a localized oxygen-depleted region that sets up an oxygen differential cell. The metal under the deposit becomes anodic while clean nearby metal stays cathodic.

Deposits create occluded zones where oxygen availability changes from one location to another, setting up oxygen differential cells that drive localized attack. Thick insulating scale, settled solids, and biofilm all create the sheltered conditions that initiate this pitting. It is a recurring endpoint of the solids and scale cascades, and the reason a chemically acceptable bulk water can still fail at the surface.

Related concepts

Deposition · Tubercle · Microbiologically influenced corrosion (MIC)

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Part of The Blueprint of Water · ⚡ electrochemistry