Marina Delucchi

Metallic structures in service in seawater are protected by coupling cathodic protection and paints, where the former may induce disbondment of the latter. A preliminary evaluation of the cathodic disbondment risk can be made by cathodic disbondment tests (CDTs). Many CDTs use cathodic potentials as large as E < −1400 mV versus saturated calomel electrode (SCE) applied up to 90 days. Only two CDT protocols require contemporary anode isolation, current and pH monitoring, without its correction. These three aspects were considered to develop a hybrid CDT; it consisted of polarizing steel panels at −1500 mV versus SCE for 12 weeks. The chemical effects related to the anodic processes were investigated. A pH acidic shift was observed and was justified by the increasing current demand due to paint damage and brucite precipitation on the panels. The necessity of anode isolating glass to prevent chlorine chemical attack against the paints, potentially affecting the disbondment result, was verified by estimating the virtual chemical attack induced by free chlorine. In conclusion, current monitoring, pH control and anode isolation are highly suggested to correctly conduct and interpret the cathodic disbondment results when CDTs requiring large electronegative potentials are applied for long periods.