Comparative Study of Cathodic Protection Effects on Corrosion and Biofouling of Bronze Alloys in Marine Environment and Laboratory Conditions

Cathodic protection (CP) is used in the marine industry to prevent corrosion of metal components in seawater but may also promote biofilm formation. When steel and copper alloy components are in contact, the latter is often subjected to higher applied CP voltages than otherwise required when a steel component is not present. In this study, the protection that CP offers in bronze alloys (RG-10 and CC492K) was assessed, both in controlled laboratory conditions and in real marine conditions in the Bay of Biscay (up to 3000 h), with various temperatures and methods: sacrificial anodes and impressed currents under different voltages. After the exposures, visual, scanning electron microscopy (SEM), X-ray diffraction (XRD) and corrosion rate analyses were performed. The results showed faster biofouling deposition on surfaces with a higher CP voltage, exposed to marine seawater, at the early stages. Subsequently, for longer exposure times, intermediate CP voltages offered less biofouling protection. XRD analyses showed the presence of calcareous compounds (calcite and aragonite), among others. Meanwhile, the corrosion observed in the laboratory was mediated by the amounts of deposited salts, with higher corrosion corresponding to higher CP voltages. Changes in temperature for the same CP voltage caused quantitative and qualitative differences in salt deposition. The higher Pb content of the CC492K alloy compared with the higher Cu and Sn contents of GR-10 did not manifest at the biofouling level, but different corrosion rates were measured (GR-10 < CC492K). Thus, the optimal CP protection conditions for marine and laboratory environments are not the same, because of the different conditions involved.