Corrosion of Carbon steel in Tap Water （Ⅰ）New Corrosion Index Based on Water Quality

Abstract

A new method to evaluate the corrosivity of tap water to carbon steel has been proposed. Corrosion tests for the tap waters sampled at 49 locations throughout Japan were conducted. Average corrosion rate v_w and maximum one v_max were measured. Relatively close relationship of v_w and v_max to concentration of SiO₂ and SO₄^2－ were found. On the other hand, the corrosion rates showed slight dependence on concentrations of Cl^－ and HCO₃^－. These facts are contradictory to the conventional knowledge. Furthermore, the authors surmised that [SO₄^2－]/[SiO₂], named SS ratio, was an effective Corrosion Index. SS ratio showed closer relationship to v_w and v_max than Langelier Index, Ryznar Stability Index and Larson-Skold Index. The authors succeeded in expressing v_w and v_max as a function of only SS ratio.