Scaling and corrosion damage of mild steel and low alloy steel in boiler feedwater

Initial corrosion of mild steel and low alloy steel in boiler feed water results in corrosion restraining oxide layers. Experiments on formation of these layers in flowing (up to 4 m/s) simulated feedwater (up to 180 deg C) are presented. According to the oxygen content of the water and depending on the hydrodynamic conditions in the tubes three different types of layers were observed. Mechanism of formation and the effect of formation are discussed. Chloride can be damaging to the corrosion restraining or protecting effects of the oxides. The different effects of chloride contaminations are discussed for the three types of layers. (author)