Corrosion control by pH

Definition

Carbon steel in a closed loop relies on a thin protective film of magnetite that holds together in alkaline water and dissolves as pH falls. Letting a loop drift toward neutral invites the steel to redissolve its own iron.

Magnetite, iron oxide, is stable only under alkaline conditions, so pH control is what keeps the protective layer intact. A drift toward neutral pH puts the system’s own iron back into solution, accelerating corrosion. This is another instance of pH deciding which chemistry runs rather than being just a logged number.

Related concepts

Corrosion inhibitor · Magnetite protective film · pH controls chemistry

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Part of The Blueprint of Water · 🧱 materials