Corrosion Types
The book frames corrosion as an electrochemical circuit (anode, cathode, electrolyte, metal path) and then catalogs the localized forms that appear once a passive film is broken and the circuit reorganizes itself. This table covers the corrosion types the book names, each driven by voltage rising and resistance falling at a concentrated site.
| Type | Primary driver | Where it occurs | Signature | Mitigation |
|---|---|---|---|---|
| Uniform (general) corrosion | Intact corrosion cell across a passivated surface | Broad metal surfaces in open water | Even thinning, loose oxide film, red-brown rust | Passivation, cathodic and anodic control, oxygen removal |
| Pitting corrosion | Film failure that concentrates voltage at a small anode | Points where passive film is breached | Deep, localized holes rather than even loss | Stabilize passive film, control chloride, maintain inhibitor levels |
| Oxygen differential corrosion | Uneven oxygen (aerated rim as cathode, starved base as anode) | Inside pits, crevices, under gaskets | Acidic, salt-rich pit that drills fast, small anode driven by large cathode | Reduce oxygen gradients, control chloride, avoid crevices |
| Under-deposit corrosion | Deposit creates local oxygen-depleted zone | Under scale, sludge, biofilm, suspended solids (cooling towers) | Hidden attack beneath deposits, quiet and persistent | Keep surfaces clean, disperse deposits, control fouling |
| Microbiologically influenced corrosion (MIC) | Bacteria (SRB, iron-oxidizing) altering local chemistry under biofilm | Systems with high microbial load, low-flow zones | Aggressive localized attack, telltale sulfur smell | Biocides, biofilm control, remove deposits |
| Galvanic corrosion | Two dissimilar metals coupled in an electrolyte | Junctions of metals far apart on galvanic series | Rapid loss of the less noble metal, worse with small anode, big cathode | Dielectric unions, match metallurgy, avoid unfavorable area ratios |
| Erosion (flow) corrosion | Shear and turbulence stripping the protective film | Elbows, tees, pump impellers, valves, exchanger inlets | Attack at high-velocity or turbulent geometry | Manage velocity and geometry, allow film to reform |
| Acid (chemical) corrosion | Low pH protonating and dissolving the oxide film | Zones of transient or sustained acid exposure | Film dissolves in minutes, accelerated anodic reaction | Maintain pH within film-stable window, buffer acid excursions |
Part of The Blueprint of Water