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Electrical Resistance (ER) for Corrosion Monitoring

The electrical resistance technique is one of the most widely used methods for measuring material loss occurring in the interior of plant and pipelines. This technique operates by measuring the change in electrical resistance of a metallic element immersed in a product media relative to a reference element sealed within the probe body. Since temperature changes effect the resistance of both the exposed and protected element equally, measuring the resistance ratio minimizes the influence of changes in the ambient temperature. Therefore, any net change in the resistance ratio is solely attributable to metal loss from the exposed element once temperature equilibrium is established.

If the corrosion occurring in the vessel under study is roughly uniform, a change in resistance is proportional to an increment of corrosion. Although universally applicable, the ER method is uniquely suited to corrosive environments having either poor or non-continuous electrolytes such as vapors, gases, soils, "wet" hydro-carbons, and non aqueous liquids.

An ER monitoring system consists of an instrument connected to a probe. The instrument may be permanently installed to provide continuous information, or may be portable to gather periodic data from a number of locations. The probe is equipped with a sensing element having a composition similar to that of the process equipment of interest. The sensing element itself can be manufactured in one of many geometries: