Fundamental fact of corrosion: it's 100% "battery" electrochemistry; without exception. That "battery" can be enhance by chemicals in the environment e.g. rust

Fundamental fact of corrosion: it's 100% "battery" electrochemistry; without exception. That "battery" can be enhance by chemicals in the environment e.g. rust on cars from salt on roads or it happens naturally as the "device" was manufactured (e.g. dissimilar metals in plumbing such as copper and galvanized steel piping).