The mechanism and the condition of occurrence in the erosion-corrosion damage of carbon steel by gas-liquid two-phase flow.

Abstract

The erosion-corrosion characteristics of carbon steel commonly used as piping material subjected to an impinging gas-liquid two-phase flow under various pH. chloride ion concentration and flow rate combinations were investigated. Environmental condition saffected not only the damage rate but also the type of damage. One of these was the enhanced general corrosion observed mainly under high chlorine ion concentration (1220ppm) and another was flow-induced pitting corrosin observed under the pH7-[C1-] 140ppm condition. Each condition of the chemical solution had its own flow effect. For example, in the case of high chlorine ion concentration, high flow rate accelerated corrosion damage by decreasing diffusion control. On the other hand, under low chlorine ion concentration, high-speed flow decreased the corrosion rate by the action of removing nonprotective oxide layer. To indicate the condition of occurrence for enhanced corrosion damage, a two-dimensional chart which had axes of [C1-] concentration and flow rate was constructed for each pH value.