Abstract
Existing guides to bimetallic corrosion are based mainly upon user experience, and data for a specific couple are given only as arbitrary ratings. However, modern developments in microelectronic circuitry have made it possible to measure galvanic current with precision and thus determine bimetallic corrosion rates in a quantitative manner. Such measurements, using a zero resistance ammeter and made on metals coupled at different anode/cathode area ratios, have formed a basis for the calculation of bimetallic corrosion effects for specific design projects. In practice, systems often have complex geometries, with the result that the effective area ratio differs from the physical area ratio owing to resistive losses in the electrolyte. In addition, real systems frequently consist of more than two different metals, so that data relating to simple bimetal combinations may be inadequate for the estimation of corrosion rates. Recent studies have shown that it is possible to develop mathematical models that make it possible to calculate the magnitude and distribution of corrosion rates in such systems. The application of such modelling techniques is illustrated for bimetallic corrosion in a mixed metal heat exchanger, and for the extent of cathodic protection down a copper alloy pipe system.
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