A case study of a corroded cast iron water main on Bridge RD, Richmond

Corrosion of cast iron water pipes, particularly localized pitting corrosion, can propagate leaks and bursts of pipelines which can lead to expensive repairs or replacement. One of the primary mechanisms which cause localized pitting corrosion within potable water networks is microbiologically influenced corrosion (MIC) due to the action of biofilms on the pipe surface. City West Water (CWW), one of the four water companies servicing Melbourne, conducts an ongoing condition assessment program of its potable water pipelines. One of the non destructive testing technologies CWW uses as part of this program on its critical water mains to assess extent of corrosion is magnetic flux leakage (MFL). The information from this program feeds back into CWW's asset management risk model and subsequently the water mains renewal program. In December 2014, a section of water main located at Bridge Rd in Richmond, Victoria was excavated as part of the condition assessment program. Soil samples and samples of the corrosion product from this in service pipeline were taken for further investigations to identify the microbial species present. From these samples microbial DNA was extracted and amplified which was confirmed via spectrophotometry and DNA gel electrophoresis. There is potential for these techniques to be expanded to a new non destructive testing technique for infrastructure to determine the presence of MIC. By comparing MFL results, soil analysis data and the early stage microbial data, the aim of this investigation is to give a more complete understanding of the environment surrounding a pipe and how this may contribute ultimately to pipe failure as a result of corrosion. A better understanding of the environment and condition of pipelines through a range of non destructive testing and how this correlates with the corrosion mechanisms occurring could lead to strategies for improved durability design and maintenance.