ABSTRACT

ABSTRACT 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. INTRODUCTION There is often a need in structures or equipments used for marine applications to mix materials, which may result in galvanic corrosion for the less noble materials. Galvanic corrosion occurs when two dissimilar metals or alloys are in electrical contact in a conductive and corrosive electrolyte. The more electrochemically active of the two metals will thus exhibit an accelerated corrosion rate. The detailed mechanisms of galvanic corrosion are well detailed elsewhere.1 The parameters influencing the galvanic corrosion are relatively well known and the extent of corrosion will depend on (a) the area ratio of the two metals, (b) the difference in their respective open-circuit potentials, and (c) the cathodic efficiency of the more noble metal. However, the readily-available information to operators and designers is often restricted to galvanic tables (i. e. seawater galvanic series) which list metals and alloys with regards to their electrode potentials in a given environment.2

This content is only available via PDF.
You can access this article if you purchase or spend a download.