Interaction between Cathodic Protection and Microbially Influenced Corrosion.

Abstract

The present work studied the interaction between cathodic protection and microbiallyinfluenced corrosion (MIC) on the surface of mild steel. Potential trending wasobserved when the currents were held constant, and current trending was observedwhen potentials were held constant. Scanning electron microscopy and energydispersive x-ray spectroscopy were used to study surface deposits on the samples andfurther understand the result of the interaction. Sulfate reducing bacteria (SRB) werethe main MIC factor studied in this work. The potentials of interest were the protectioncriteria of -850 mV vs copper-copper sulfate electrode (CSE) generally recommended toprotect buried or immersed steel and the -950 mV (CSE) recommended for cathodicprotection of steel exposed to risk of MIC.The results obtained from the experiments suggest the following main findings:- The activities of SRB underneath a biofilm caused ennoblement of potential ifthe current is held constant.- It also caused increase in current required to cathodically polarize metal surfaceat a specified potential.- Cathodic potentials did not have effect on attachment and viability of SRB onmetal surfaces in the range of potential studied in this work.The cathodic potential of -950 mV (CSE) recommended for cathodic protection underrisk of MIC appeared to have effect of reducing the probability of deposition of ironsulfide, one of the main factors in corrosion acceleration for MIC. Furthermore, theformation of calcareous deposit helped reducing the current demand in cathodicprotection under this potential, although SRB are still viable on the metal surface.

Date of Award	31 Jul 2012
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Robert Cottis (Supervisor)