On the possible identification of biocorrosion in water supply systems

Summary

The results of the analysis of the literature data and in-house studies of steel cold and hot water pipelines subject to internal corrosion are presented. The common factor for all the studied samples was the occurrence of corrosion tubercles along the pipe inside perimeter. The study of tubercular deposits with the help of scanning electron microscopy allowed identifying four typical zones: base, core, hard coat and thin surface layer. These zones differ in structure and chemical composition. The mechanism of electrochemical and microbial induced corrosion of steel pipes is described. It is assumed that the zone under the tubercle consists of numerous corrosion electrochemical elements. On the outer edge of a tubercle corrosion occurs with oxygen depolarization, whereas inside – with hydrogen one; at that, the potentials arising during oxygen depolarization are producing a dominant effect on the formation of the outer dense layer. The hypothesis of the mechanism of tubercular deposits growth and their typical morphology is presented. On the basis of studying the properties of the deposit samples taken from the operating pipelines with the purpose of restoring the conditions of their formation the assumption on the dominant effect of microbial induced corrosion on the pipe material was made. Identification of the bacteria role in corrosion process, apart from the direct observations, can be made on the basis of determining crystalline ferric oxides formed on the surface of bacterial cell remains and their magnetosomes. The definite answer to the question on the decisive role of bacteria in corrosion of metal pipelines requires further studies.

Key words

water supply , corrosion deposits , biofilm , microbial induced corrosion , steel pipes , energy-dispersive analysis , scanning electron microscopy