Abstract
Uncertainties are present about the mechanisms of cathodic protection (CP) and its effectiveness to limit or completely stop Microbiologically Influenced Corrosion (MIC). The goal of this research was to improve the understanding of the mechanisms of CP by determining the interactions between corrosion and local chemical parameters, such as pH, under varying CP conditions, both in the absence and presence of MIC.
Electrical resistance (ER) probes, covered with a biofilm of sulphate-reducing microorganisms, were subjected to a series of CP potentials. In some cases MIC could not be stopped by CP, even at very negative potentials. The application of CP potentials resulted in an increase of the pH near the steel surface. In the absence of a biofilm CP could raise the pH above 13, whereas the pH remained below 8 in the presence of an active MIC biofilm. These findings show that MIC biofilms can reduce the effectiveness of CP by maintaining a mild pH, supporting their activity.
Once biofilms have established, it may be very hard or even impossible to stop MIC with CP, irrespective of the potential applied. This suggests that CP strategies should be aimed at preventing MIC biofilms to develop from the start.
