Corrosion of steel by chlorinated water
Centeno, Rafael Jose
Harkins, C. Girvin
Master of Science
Conflicting literature reports on the influence of chlorination treatment on the corrosion of steel in water suggested the need for a careful study combining both materials science and electrochemical approaches. Steels of grades 12 and 15 were mounted in thermosetting polymer, polished, and metallurgically characterized. These mounted samples were then made the anode in a well-stirred, gas-purged electrochemical reactor described in the thesis. Distilled water containing 25 g/1 of ISO served as supporting electrolyte. A commercial electrochemical instrument (Beckman Electroscan 3P) provided both power supply and recording functions for obtaining potential-current corrosion response curves. In addition, the instrument recorded pH and Cl concentration. Corrosion rates and passivation effects as a function of these variables resulting from chlorination are reported and discussed, as are the visual observations of the corroding steel surface. Under similar conditions, the two steels showed quite different corrosion behavior and surface appearance. For steel 12, the corrosion rate was generally larger with chlorination of water and the surface became bright on passivation. For steel 15, a decrease in corrosion was observed with high chlorine content and the surface formed a black film rather than a reflective film upon passivation. Passivation for 15 occurred at more negative electrochemical potentials upon chlorination. In general, the zone of potentials over which passivation was observed (before the transpassive zone appeared) was smaller in chlorinated water than in the supporting electrolyte. This thesis is one of the very few systematic studies of this common materials/environment combination, and probably the first to report on the interaction between carbon content in steel and chlorine content in water. The results affirm the complexity of this system, make plausible the conflicting results of earlier authors, and suggest additional experiments.