EFFECT OF INORGANIC SULFIDE AND BACTERIAL MICROFOULING ON CORROSION OF 70/30 COPPER/NICKEL ALLOY IN SEAWATER

摘要

A laboratory investigation was carried out on the effect of sulfate-reducing bacteria (SRB) and 1 ppm inorganic sulfide on the corrosion behavior of 70/30 Cu-Ni alloy in seawater. Potential/time and linear polarization measurements showed that the presence of SRB makes the corrosion potential more active and increases the corrosion rate. On the other hand, the addition of sulfide caused significant ennoblement in the corrosion potential which was associated with a small decrease in the corrosion rate. SRB had a pronounced effect on the potentiodynamic polarization through shifting the corrosion potential to a more active value and eliminating the active/passive transition. However, the active/passive transition peak was retained when sulfide was added to seawater inoculated with bacteria. With the increase in exposure time to seawater inoculated with SRB, the impedance and phase angle peak decreased. In presence of 1 ppm sulfide, the impedance increased in the high frequency region and the frequency dependence of the phase angle showed two time constants. SEM examinations revealed the formation of a patchy layer of bacterial biofilm and corrosion products during exposure to SRB-containing seawater. The formation of this layer was associated with depletion of nickel from the alloy. In the presence of inorganic sulfide, micropits and intergranular attack were seen within crevices in an adherent corrosion product layer.