The galvanic corrosion of carbon steel (UNS G10150) and of copper-nickel 90/10 (UNS C70600) coupled to superduplex stainless steel (UNS S32750) in seawater was investigated from 6°C to 70°C, with different cathode to anode ratios. The effect of chlorination on galvanic corrosion rates was also studied. Continuous monitoring of the open-circuit potentials and galvanic currents were performed to measure the exact evolution and the contribution of the galvanic corrosion on the total corrosion. Results showed that formation of natural biofilms and precipitation of calcareous deposits on surfaces had a very significant impact on the cathodic efficiency, which is directly correlated to the rate of galvanic corrosion. For all the tested configurations, chlorination led to a significant decrease of the measured galvanic currents due to the low cathodic efficiency of surfaces in chlorinated media (i. e. no biofilm). The long term exposure of specimens allowed to draw realistic pseudo-polarization curves which were used in a boundary element modeling software.