The galvanic corrosion of carbon steel (AISI. 1015) and of copper-nickel 90/10 (C70600) coupled to superduplex stainless steel (AISI. F-53) in seawater was investigated from 6°C to 70°C with different cathode to anode ratios. The effect of chlorination and of tri-material coupling on galvanic corrosion rates was also studied. The continuous monitoring of the open-circuit potentials together with galvanic currents was performed and allowed measuring the exact evolution and contribution of the galvanic corrosion on the total corrosion. Results clearly showed that the formation of the natural biofilm and that the precipitation of calcareous deposit on surfaces had very significant impact on the cathodic efficiency which is directly correlated to the galvanic corrosion rates. For all the tested configurations the chlorination led to significant decrease of the measured galvanic currents due to the low cathodic efficiency of surfaces in chlorinated media (i. e. no biofilm). Tri-material coupling (e.g. carbon steel CuNi 90/10 and superduplex stainless steel) was also tested using different surface ratio of the materials. However the tri-material coupling did not lead to higher corrosion rates than the one measured on bi-metallic couples. Finally a model derived from the results using boundary element software is discussed.