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IV. ER Technique - General
A. Measurement Theory
The reduction in cross-sectional area of an element of metal or alloy as it corrodes is accompanied by a
corresponding increase in the electrical resistance of the element. The relationship is given by:
R = p x L/A .......................................(6)
R = element resistance
P = specific resistivity of the element alloy
A = element cross-sectional area
L = element length
Consequently, periodic resistance measurements of a metal/alloy element that is continuously exposed to
a corrosive environment, will provide data on the rate and extent of corrosion for that alloy/environment
combination.
In practice, resistance is also a function of temperature. Therefore, electrical resistance corrosion probes
need some means to compensate for the spurious effects of temperature change. This is achieved by
constructing the probes with an exposed element that freely corrodes and a reference element that is
protected within the body of the probe and not subject to corrosion. Such a construction is illustrated in
Figure 5.