Temperature Effects on Iron Corrosion

Temperature is an often overlooked water quality parameter that may influence corrosion of iron pipes in drinking water distribution systems. This study examined corrosion of cast iron samples in an aerobic, microbially stable water at different constant temperatures (5, 20, and 25°C) as well as in waters where the temperature continuously cycled (17.5 – 23°C and 5 – 20°C). The composition and morphology of scale formed at the three different constant temperatures showed large differences, and the 5°C experiment had more weight loss, higher iron concentrations in the water, and more tuberculation compared to 20 or 25°C. However, little difference was observed in the temperature cycling experiments. INTRODUCTION Many parameters that influence corrosion can vary with temperature: dissolved oxygen (DO) solubility, solution properties (e.g. viscosity and ion mobility), ferrous iron oxidation rate, thermodynamic properties of iron scale (leading to formation of different phases or compounds), and biological activity.1 Moreover, heterogeneous iron scale formed on pipes may have large differences in physical properties such as scale density (as described by the Pilling-Bedworth ratio, PBR) and coefficients of thermal expansion.2 If the scale is exposed to temperature gradients or cycling, these differences might cause mechanical stresses in the scale, leading to spalling or sloughing of scale into the water as corrosion by-products. Only a few studies have examined the role of different temperatures in distribution system iron corrosion. In general, studies of distribution systems found the manifestations of corrosion to be less severe in colder winter months; for example, lower iron concentrations and corrosion rates3 and fewer customer complaints of red water4, 5 were observed in winter. Also, one laboratory study found decreased weight loss for iron samples held at 13oC versus 20oC.6