Abstract
The corrosive behaviors of waters with different calcium carbonate saturation indices were evaluated using mild steel in jar tests which utilized a weight loss method. The corrosivity of the waters were assessed to determine whether the Langelier Index, as widely used in the drinking water industry, is a reliable indicator of a water's corrosive potential. No definite relationship was found between corrosion rate and Langelier Index. Similar conclusions could be drawn from corrosion studies in loop systems. Waters with positive Langelier Indices were sometimes as corrosive as those with negative values. Wet chemical and X-ray diffraction analyses of corrosion products from black steel pipes used in the loop studies revealed that calcium carbonate precipitated with the metal oxides irrespective of the saturation index of the water. An empirically formulated model which defines relative corrosion rate as a function of chloride, sulfate, alkalinity, dissolved oxygen, calcium, buffer capacity, saturation index, and exposure time yielded a satisfactory graphical fit to the experimental data. Multivariate regression analysis indicated that a logarithmic mathematical model expressing corrosion rate in terms of total dissolved solids, dissolved oxygen, saturation index, and exposure time could account for 98-percent of the variation in corrosion rate under the experimental conditions employed in the study.
