Abstract
Relation between corrosion potential and distribution of localized corrosion depths was studied by the 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 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 explained as attributable 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·y-1] plotted against the corrosion potential [Ecorr/V(vs. Cu/CuSO4)] successfully gives the following relation:
P≤0.51·Ecorr+0.34
where P is the localized corrosion depth simply divided by a length of time during which a structure has been in use. Further when whole data of localized corrosion are classified by corrosion potential, the mean of and the standard deviation of distribution of localized corrosion depths are expressed by the neat functions of corrosion potential. The analysis results indicate that the corrosion potential and the exposure time have contributed to a corrosion process independently.
