An in-situ galvanically coupled multielectrode array sensor for localized corrosion

A localized corrosion sensor consisting of multiple, corrodible, miniature electrodes was tested in different chemical environments. The miniature electrodes were coupled together by connecting each of them to a common joint through independent resistors, with each electrode simulating an area of a corroding metal. In a localized corrosion environment, anodic currents flow into the more corroding electrode, and cathodic currents flow out of the less or noncorroding electrodes. These currents are measured from the voltages across the resistors. The variation among the galvanic currents measured from the miniature electrodes responded well to changes in the environment with respect to localized corrosion. It was demonstrated that statistical parameters derived from the currents flowing through the miniature electrodes, such as the standard deviation or the 90th percentile anodic value, can be used as effective indictors for localized corrosion. Measurement showed the following order of corrosiveness of the environment for UNS S30400 stainless steel: deionized water < saturated potassium chloride (KCl) < 1 M sodium nitrate (NaNO3) + 0.25 M ferric chloride (FeCl3) < 0.0025 M FeCl3 < 0.25 M FeCl3. It was also shown that the penetration rate of localized corrosion may be estimated from either the measured maximum or the standard deviation of the anodic current densities, and the cumulative penetration may be estimated from either the measured maximum or the standard deviation of the cumulative anodic charges through the electrodes.