Critical concentration of dissolved oxygen to form protective iron oxides under combined water treatment conditions

AbstractThe corrosion behaviour of carbon steel under combined water treatment (CWT) conditions was investigated for the purpose of determining the minimum adequate oxygen concentration. Corrosion tests were carried out in flowing water (pH 9.0) under simulated CWT conditions at 250° C for 500 h, and electrochemical measurements were also carried out during these test periods. The corrosion potential of carbon steel shifted in the noble direction and the polarisation resistance increased with increasing oxygen concentration in the range of 5 to 15 μg L-1. The corrosion rate calculated from weight loss measurements in oxygenated water containing 15 μg L-1 of dissolved oxygen was less than that in deaerated water. In the case of the water containing 25 μg L-1 of dissolved oxygen, the corrosion loss was much smaller than that for deaerated water. In addition, no significant change of corrosion behaviour was observed for oxygen concentrations in the range 25 to 100 μg L-1. The present work has shown that the ...