Fighting Corrosion with Electrochemistry
Cathodic protection is the most widely used active corrosion prevention technology, protecting over 3 million kilometers of buried pipelines worldwide. The principle is elegantly simple: by making the protected structure sufficiently cathodic (negatively charged), metal dissolution becomes thermodynamically impossible. The structure's potential is shifted from the active corrosion region into the immune region of its Pourbaix diagram.
Sacrificial Anode Systems
The simplest CP approach connects a more active metal — typically zinc, magnesium, or aluminum alloy — to the protected structure. The potential difference drives a galvanic current that polarizes the structure cathodically. Sacrificial systems are self-regulating, require no external power, and are ideal for well-coated structures with modest current demands. Ship hulls, water heaters, and small pipelines commonly use this approach.
Design Parameters
Proper CP design requires calculating the total protection current (surface area times required current density), then sizing anodes to deliver this current for the design life. Coating condition is critical: bare steel in seawater needs 100-150 mA/m², while well-coated steel needs only 5-20 mA/m². Soil resistivity determines how easily current flows from anode to structure — high-resistivity soils may require impressed current systems or conductive backfill.
Monitoring and Maintenance
CP systems require periodic monitoring to verify adequate protection. Structure-to-soil potential is measured against a reference electrode (typically Cu/CuSO₄), with -850 mV being the widely accepted protection criterion for steel. Over-protection below -1200 mV can cause hydrogen embrittlement and coating disbondment, so the target range is narrow. This simulation lets you design a sacrificial anode system and predict its service life.