Galvanic studies related to the use in desalination plant of corrosion-resistant materials

Galvanic currents and potentials have been measured for bimetallic couples involving carbon steel, three grades of stainless steel, 90 Cu/10 Ni and titanium when exposed to seawater in the laboratory at temperatures of 18C and 60C and varying oxygen content. The galvanic currents flowing between couples consisting of two of the corrosion-resistant materials were very small. The galvanic corrosion rate of carbon steel, when connected to one of the other materials, was dependent upon the cathodic-polarisation characteristics of the noble-material surface with indications that, at a given area ratio, the galvanic corrosion of carbon steel was greater when coupled to the 90 Cu/10 Ni alloy than when connected to stainless steel or titanium. The usual effects of increasing the anode/cathode area ratio were observed and data were obtained to demonstrate quantitatively the significant beneficial effect of coating the cathode in a bimetallic couple. Intermediate air exposures were not found to promote any large, long-term, effects on galvanic corrosion. There was evidence that galvanic corrosion rates were very small when the dissolved oxygen content was controlled at low levels and some interesting aspects of galvanic corrosion at the higher temperature were noted.