Determination of the Optimum Cathodic Protection Potentials of Common Use Metals in Seawater by their Polarization Resistances

The selection of an optimum potential value for cathodic protection is vital to the achievement of maximum corrosion suppression at minimumpower.In spite of the importance of the appropriate choice of the cathodic protection potential value for each specific case, the selection is usually made empirically, without a firm theoretical basis.Tsuru, Jeon and Haruyama indicated that the optimum cathodic protection potential coincides with the potential at which the faradaic impedance is maximum.The impedance technique can be used for both determining and monitoring the optimum cathodic protection potential, but the technique is a complicated work.The authors have recently developed a new theory of determining method that the optimum cathodic protection potential coincides with the potential at which the polarization resistance is maximum or infinite.This determining method by the new theory is very simple.It can indicate the optimum cathodic protection potential directly by the shape of the external cathodic polarization curve.This study is to verify experimentally the validity of the new theory by mean of the corrosion-loss measurement for carbon steel and brass in natural seawater.It was concluded that the polarization resistance technique is a simple and promising method for determining and monitoring the optimum cathodic protection potential for metal.