The Effect of Pollutants and Bacterial Microfouling on the Corrosion of Copper Base Alloys in Seawater

The effects of seawater contaminants such as ammonium and sulfide ions and trimethylamine on the corrosion behavior of copper base alloys have been studied. Sulfide contamination causes a long-term change in the surface properties of the passive film formed on these alloys in uncontaminated seawater. The kinetics of oxygen reduction and anodic dissolution were studied, and the results were analyzed on the basis of a simple, activated-diffusionally controlled model. It has been shown that the relationships derived for the rotating disk electrode geometry can be extended to any hydrodynamic configuration, provided the corresponding dimensionless number relationships are known. The correlating parameter (between the rotating disk experiments and hydrodynamic geometries) used in this work is the mass transfer coefficient. Bacterial contamination led to the loss of passivation, and the corrosion rate was determined by the rate of oxygen diffusion through the bacterial slime. Three genera of bacteria have been identified in the bacterial slimes present in condenser tubes using contaminated seawater as coolant. These were Pseudomonas, Micrococcus, and Corynebacterium. Of these, the Pseudomonas were entirely responsible for the observed corrosion rate increase. The combination of bacterial contamination and anaerobic conditions can create an extremely corrosive environment.