Abstract
Electrochemical noise measurement is established as a means of estimation of corrosion rate, and methods for the identification of localized corrosion have been proposed. Many of these methods make the assumption that two electrodes used to measure current noise have similar behavior; this paper examines tests based on measured data that can be used to assess whether or not the current-measuring electrodes can be assumed to be symmetrical (i.e. they have sufficiently similar behavior). It is concluded that the mean current (which should have a value close to zero) cannot be used reliably as a test for symmetry, as even small differences in the mean current from the two electrodes (and hence minor departures from perfect symmetry) will lead to a mean current that is far larger than is expected for perfect symmetry. However, the coefficient of correlation between the potential and the current noise does appear to provide a useful test for symmetry; perfect symmetry implies that the coefficient of correlation will be zero. The significance of a non-zero coefficient of correlation depends on the nature of the departure from symmetry, but values above 0.5 suggest that there is sufficient asymmetry to lead to significant errors in estimates of electrochemical noise resistance.
