This paper describes the main features and performance of a retrofitted cathodic protection (CP) system on six, 5.2 MGD multistage flash (MSF) units which has operated satisfactorily for an extremely long period. The installation of the CP system was precipitated by experience of severe corrosion on many carbon-steel components within months of commencing operation of the MSF units. An extensive impressed-current CP system was fitted to the internal surfaces of painted carbon-steel pipes, rubber-lined waterboxes and other components. After one year of operation, it was found possible to drastically reduce the number of anodes and, almost two decades later, the CP system continues to successfully control corrosion on the components. The paper describes the CP system and presents evidence from internal inspections of its effectiveness. The important features contributing to the performance of the CP system, in terms of operating parameters and economics, are discussed. In this respect, evidence is presented of the crucial role, in the corrosion-control process of the concurrent deposition of calcareous scale during operation of the CP system.