Determination of Chemical Species Dominating the Corrosivity of Japanese Tap Water by Multiple Regression Analysis

Abstract

Japanese tap water is Ca2+-poor and SiO2-rich in comparison with that of other counties. Thus, there have been few studies on its corrosivity. We sampled tap waters at 70 different sites and in different seasons in Japan, subjected the samples to chemical analysis and measured localized corrosion depth and the total corrosion loss of carbon steel placed in these waters. The average corrosion rate vavg and maximum localized corrosion rate vmax were calculated. The ratio of vmax to vavg, which was defined as localized corrosion factor LCF (=vmax/vavg), was also studied. The multiple regression method was applied to obtain the dependence of vavg (objective variable) on concentrations of chemical species (explanatory variables). In the same manner, the relation of vmax and LCF to concentrations of chemical species was derived. As a result, we showed that SiO2 and SO42− mainly dominate the corrosivity of Japanese tap water. In particular, as SO42− increased, vavg became larger and vmax became smaller. Also, as SiO2 increased, vmax became larger and vavg became smaller. The behavior of LCF was similar to that of vmax. The findings of this study will be useful for estimating the corrosivity of tap waters that have low Ca2+ and high SiO2 concentrations.