Disbonding of underwater-cured epoxy coating caused by cathodic protection current

Cathodic disbonding of the underwater-applied, ultra-thick, solvent free epoxy coating subjected to various levels of cathodic protection was investigated during the period of the coating cure. The results indicate that the partially cured coating was of low resistivity, between 103 and 105 Ω cm2 for the cathodic polarization of on-potentials between −0.98 and −1.4 VAg/AgCl/sw. The coating was shown to be capable of withstanding normal levels of cathodic protection between off-potentials of −0.8 and −1.1 VAg/AgCl/sw while the IR drop, introduced by the coating in the same potential range, increased from 0.06 to 0.1 V and has to be taken into account at the design stage of the cathodic protection system. Beneficial influence of calcareous deposit formation on the cathodic protection current was confirmed, particularly for the failed coating. The initial period (1 week) of coating cure was shown as the most critical for disbonding processes caused by the excessive cathodic polarization.