The effect of hydrogen on the corrosion of a 2.25% Cr ferritic steel by high temperature water

Abstract

The effect of maintaining a high concentration of hydrogen in the vicinity of 2.25%Cr ferritic steel surfaces undergoing corrosion in high temperature water (345°C) has been investigated. In 1000 h tests in a flowing water loop, a high level of hydrogen was found to increase the rate of corrosion by a factor of 3, prevent formation of an outer layer of magnetite and result in the deposition of copper metal. The first two of these observations are attributed to a local increase in magnetite solubility, brought about by the high hydrogen concentration. Water at the surface is therefore undersaturated with dissolved iron (although the bulk of the loop water is supersaturated with iron) and the more soluble regions of the inner spinel layer dissolve away. Thermodynamic considerations indicate that copper, present in solution (≤ 1 ppb) in equilibrium with CuO, is precipitated out as the less soluble Cu metal, because of the highly reducing conditions at the surface.