Definition
A form of electrochemical corrosion that occurs on a metal surface when two areas of that surface are exposed to electrolytes of different concentrations, or to differing amounts of oxygen. The variation between the two areas creates a small electrical current within the metal, and the area with the lower oxygen concentration becomes the anode and corrodes away. It commonly forms in tight crevices, under gaskets, beneath lap joints, and in any location where moisture or contaminants can be trapped against the metal.
Plain English
Corrosion that happens when one part of a metal surface is exposed to a different amount of moisture or oxygen than the part right next to it. The difference sets up a tiny electrical reaction, and the metal in the starved area eats itself away. It usually hides in tight spots where dirt and water get trapped.
Context Anchor
Seen in aircraft corrosion inspection, especially in seams, lap joints, under fasteners, under gaskets, and anywhere moisture or dirt can stay trapped against metal.
Derivation
Concentration here means the amount of a substance (oxygen or electrolyte) present in a given area. Cell refers to an electrochemical cell -- the same kind of small battery-like reaction that occurs in any corrosion process. So the term literally describes a corrosion cell driven by differences in concentration between two spots on the same piece of metal.
Why Pilots Care
It can silently weaken aircraft aluminum structures in hidden areas such as under sealant or in crevices, leading to expensive repairs or airworthiness issues if missed during inspections.
Analogy
It is like two spots on the same piece of metal being connected to two different tiny battery conditions. The spot in the worse condition pays the price by losing metal.
Grounding Statement
Picture moisture trapped under a dirty seam: the covered area gets less oxygen than the exposed area, and that difference can start corrosion.
Intuition Check
Do not read “cell” as a living cell or a spreadsheet box here. In this term, “cell” means a tiny electrical action that can make metal corrode.
Example Sentence 1
The mechanic found concentration cell corrosion under the wing skin lap joint where rainwater had been wicking in for months.
Example Sentence 2
Frequent washing of the aircraft helps prevent concentration cell corrosion from starting in areas where moisture collects.