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Cathodic Protection and MIC - Effects of local electrochemistry

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The goal of this research was to improve the understanding of the mechanisms of cathodic protection (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.

Product Number: 51317--9452-SG
ISBN: 9452 2017 CP
Author: Stefan Jansen
Publication Date: 2017
Industry: Cathodic Protection
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Uncertainties are present about the mechanisms of cathodic protection (CP) and its effectiveness to limit or completely stop microbiologically influenced corrosion (MIC). An uncertain but probably crucial factor is the role of environmental conditions and the ensuing electrochemical and microbiological reactions. 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 and Fe2+ 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 exposed to anaerobic groundwater and subjected to a series of CP potentials both in the laboratory as well as in the field. We observed that MIC could in some cases not be stopped by CP even using very high applied potentials. Detailed measurements with microsensors were used to obtain information on small scale chemical gradients near and in the MIC biofilm growing on the steel surface of an ER probe.The results show that CP resulted in an increase of the pH near the steel surface. In the absence of microorganisms 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 active MIC biofilms influence the effectiveness of CP. This implies that it is not possible to give one general criterion for a potential at which MIC will always be stopped.Once certain biofilms have established it can 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 instead of stopping an already established biofilm.

Key words: MIC, electrical resistance probe, cathodic protection, biofilm, sulphate-reducers, microsensors, pH, electrochemistry

Uncertainties are present about the mechanisms of cathodic protection (CP) and its effectiveness to limit or completely stop microbiologically influenced corrosion (MIC). An uncertain but probably crucial factor is the role of environmental conditions and the ensuing electrochemical and microbiological reactions. 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 and Fe2+ 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 exposed to anaerobic groundwater and subjected to a series of CP potentials both in the laboratory as well as in the field. We observed that MIC could in some cases not be stopped by CP even using very high applied potentials. Detailed measurements with microsensors were used to obtain information on small scale chemical gradients near and in the MIC biofilm growing on the steel surface of an ER probe.The results show that CP resulted in an increase of the pH near the steel surface. In the absence of microorganisms 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 active MIC biofilms influence the effectiveness of CP. This implies that it is not possible to give one general criterion for a potential at which MIC will always be stopped.Once certain biofilms have established it can 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 instead of stopping an already established biofilm.

Key words: MIC, electrical resistance probe, cathodic protection, biofilm, sulphate-reducers, microsensors, pH, electrochemistry

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