Impressed current cathodic protection - Development of optimum system configurations for ships using scale models (physical scale modelling)

The purpose of this fundamental study was to establish optimum cathodic corrosion protection system configurations for ship hulls. Comprehensive surveys were conducted in order to develop a better understanding of the electrochemical processes occurring on a ship hull in a seawater electrolyte. The results obtained show that the performance of a system can only be evaluated when it is installed on a real object. However, once installed the location of the impressed current anodes and the reference electrodes cannot be changed if the potential distribution over the underwater hull is not optimal. Hence, a procedure had to be established that permits the development and optimisation of system configurations for future objects. A validated, experimental laboratory technique using scale ship models was established to determine the fundamentals of cathodic corrosion protection and to develop a theoretical understanding of the underlying mechanisms. The findings obtained in practice could be applied to the models. The model studies were conducted in a systematic manner and under defined conditions in German standard (DIN) artificial seawater and in a natural electrolyte. The experiments clearly showed the functional correlation between the geometric configuration of the reference electrodes on the hull and the locations of the anodes. The results reflect the interrelationships between the electrochemically more positive bronze propeller and the steel. The configuration developed in the course of the experiments provided an optimum distribution of the protection current over the entire hull model. The data from the model study were applied to the design features of the Class 123 Frigate. Subsequently, the efficiency of this procedure was evaluated on a real object in a real electrolyte. The results obtained clearly demonstrate that physical scale modelling is a rational, scientific method for the evaluation and design of impressed current cathodic protection systems.