Corrosion of carbon steel in solutions containing free chlorine in similar concentration to that used in drinking water sanitation

In the production of drinking water, disinfection is essential to guarantee its quality, and is mainly carried out by adding free chlorine (FC). In the present work, the corrosion resistance of ASTM A1018 steel, used in the drinking water distribution system in the state of São Paulo, Brazil, was investigated in a solution containing 3.0 mg L −1 of residual FC. The results of the characterization of the corrosion products layer showed that it has a bilayer structure comprised of an internal adherent magnetite layer and a top layer of lepidocrocite, which is gel-like and non-adherent. For the immersion time investigated, the results of the electrochemical impedance spectroscopy tests showed low corrosion resistance and indicated that the steel responds as a porous electrode with finite pore length, obeying the de Levie theory only in the high frequency region.