Relation between Corrosion Potential and Depth Distribution of Localized Corrosion on the Inner Surface of a Steel Water Channel

摘要

The relation between corrosion potential and distribution of localized corrosion depths was studied using statistical analysis. Corrosion potentials and depths of localized corrosion under tubercles were measured at 27 survey sites on the inner surface of two steel water channels in which river water flowed.The results showed that there was poor correlation between the maximum localized corrosion depth and corrosion potential with regard to the respective survey sites. At five sites where corrosion potentials were almost at the same level, depth distributions differed from each other significantly. This difference can be attributed to variation of exposure time of the steel surface to water after the rupture of a coating film. The above results suggest that the extreme value statistical analysis is not always applicable even when the corrosion potential of the respective survey sites is identical. However, P (mm centre dot y~(-1)) plotted against the corrosion potential (E_(corr)/V (vs. Cu/CuSO_4)) successfully gives the following relation:P<=0.51 centre dot E_(corr)+0.34where P is the localized corrosion depth simply divided by a length of time during which a structure has been in use. Further when the entire data of localized corrosion is classified by corrosion potential, the mean and the standard deviation of distribution of localized corrosion depths are expressed by the neat functions of the corrosion potential. The results of the analysis indicate that the corrosion potential and the exposure time have contributed to the corrosion process independently.