Can an intermittent cathodic protection system prevent corrosion of buried pipeline?

Carbon steel pipelines are provided with corrosion prevention systems, namely an insulating coating and a cathodic protection (CP) system that reduces corrosion rate below 10 μm/a. CP is applied by a stationary cathodic current, which effectiveness on the metal surface is twofold: oxygen consumption and alkalinization (pH > 10) at the metal-to-electrolyte interface. The increase of pH is beneficial, promoting passive condition. In this paper, a preliminary study of the effect of intermittent CP has been carried out in order to investigate the effect of a temporary current interruption on the potential monitoring and on the residual corrosion of the metal. During the on period, oxygen is consumed and alkaline pH is established, during off period, the alkalinity and the slow oxygen replacement assure corrosion rates lower than in free corrosion condition. Test has been performed both in normal and overprotection condition, varying the off period duration, monitoring weekly the protection potential.