The influence of dissolved oxygen concentration on the corrosion of grey cast iron in water at 50°C

Abstract

The formation of corrosion scales has been studied on grey cast iron in flowing water at 50°C as a function of O 2 concentrations from 0.1 to 3.95 ppm O 2. Below 1.0 ppm O 2, nodular scales form containing Fe 3O 4 and a green rust, GR. At higher O 2 concentrations, a continuous scale eventually forms, consisting of a porous subscale of Fe 2O 4 + GR overlaid with a compact crust of Fe 3O 4 + GR and a thin surface layer of γ-FeOOH. ‘Chimneys’ oriented in the water flow direction grow out of the crust. γ-FeOOH is reduced to Fe 3O 4 which becomes the principal constituent of the scale. Scales on cast iron components from central heating systems closely resemble those found in the present work.