EFFECT OF BIOFOULING ON CATHODICALLY PROTECTED CARBON STEEL IN SHALLOW SEAWATERS EXPOSED TO SUNLIGHT PHOTOPERIOD

Here presented research deals with carbon steel samples cathodically protected with Zinc anodes controlling applied potential with resistances in the window for oxygen limiting discharge (-850±50 mV Ag/AgCl). Characterization of biofouling effects was made through comparison between electrodes immersed in aged tank of natural seawater and a control tank filled with not biologically active seawater. Both tanks were exposed to sunlight photoperiod for several days during the summer 2008. Cathodic current behaviours were monitored during dark hours, sunlight hours and during sunlight interruptions via temporary tank coverage. Observed variations showed that the biolayer induces appreciable and diversified effects. Particularly, these are considered to be induced by active contribution (O2 production/consumption cycles) and passive contribution (O2 diffusion shielding from the bulk), in addition to the passive one performed by underlying calcareous deposit per se growing under cathodic polarization in seawaters.