Role of Surface Structure and Flow Rate on the Polarization of Cathodically Protected Steel in Seawater

In an earlier report,2 a semi-empirical model was developed describing the relationship between current density (CD) and time on cathodically protected steel in seawater. Experimental studies performed presently with prerusted and polished steel specimens exposed to natural seawater in a flow channel indicate that the effects of flow and the initial surface structure of steel can be correlated with the initial limiting CD resulting from oxygen reduction. The results also demonstrate the importance of the geometry of the steel cathode in determining the polarization behavior. An analysis of these and other available polarization data indicates, in particular, that the ratio between the initial values of impressed CD and limiting CD has to be more than 0.3 to assure polarization in the North Sea. The mathematical model is modified to incorporate these effects.