Study Of The Galvanic Corrosion Under The Simulated Conditions Of Deep-sea Environment

Materials with different electrochemical characteristics will be evitably in touchwith each other for the demand of structure and performance in the marine conditions.This situation will obviously accelerate corrosion of metals owe to the galvaniccorrosion in the solutions containing chloride ions. For several decades, experts havestudied large number of the corrosion behaviors and protective measurements ofmaterials and its constructional element which immersed in the surface seawater.However, it is indicated that the conditions in the deep-sea, including illumination,temperature, pressure, dissolved oxygen, pH, salinity and flowrate etc., were quitedifferent from that of surface, which affect the corrosion process of metals in differentways. It is necessary, for the datas obtained from the surface, to test and verify thesecurity that applied in the deep. To solve this problem, the corrosion testing ofmaterials and its components should be carried out to get and accumulate the laws ofcorrosion.The materials used in this work were B10, B30, Silicon Brass, Nickel-aluminiumbronze and304stainless steel. In the first step, all the materials were studied underthe lab conditions(20℃,1atm). Galvanic corrosion tendency was predicted by thesteady-state polarization curves and the corrosion potential obtained in the seawater.Film formation and corrosion mechanism were discussed by the Atomic ForceMicroscope (AFM), Scanning Electron Microscope (SEM), Optical Microscope andSurface element analysis technology. In the second part， Electrochemical ImpedanceSpectroscopy(EIS) and polarization curves were carried out to evaluate the chemicalperformance in different temperatures and dissolved oxygen, which could provideprediction informations applying mixed potential theory. At last, the galvaniccorrosion behavior was investigated by monitoring technology together with weightlose experiment.The research shows that the corrosion potential sequence of the materials are: 304>B30>B10> Nickel-aluminium bronze> Silicon Brass. The bronze and brass arethe anodes element of the pairs because their corrosion potential is less noble than thatof copper-nickel alloys, while the304stainless steel is the cathode because of itsnoble potential. The electrochemical testing gives the facts that temperature is afactor that impacts two process of electrode at least while the dissolved oxygen affectssingle one. When controlling the oxygen saturation (≥30%) under the same conditions,the cathodic process is basiclly not or a little affected by the temperature, whileAnode passivation depend on it. The oxygen diffusion-controlled process of cathodicpolarization is weakened with the reduction of the saturation. The coupled potentialobtained from the polarization curves increases with temperature and saturation whilethe galvanic current decreases. Compaired with the datas obtained from themonitoring, the regularity is similar. Time that the galvanic current density comes tosteady decrease with temperature. The current density under50%oxygen saturation ishigher than the others. The galvanic corrosion sensitivity of B10/bronze couple andB10/brass couple are class B, that of three couples of B30are class A. the galvaniceffect decrease with oxygen saturation and increase with temperature.