51316-7850-MIC Studies of Buried Potable Water Pipelines Using Semi-Solid Agar as an Analogue for Soil

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Product Number: 51316-7850-SG

ISBN: 7850 2016 CP

Author: Amy Spark

Publication Date: 2016

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Water pipelines are a vital part of Australia’s infrastructure as they are for much of the developed world. Seventy percent of this network predominately critical transmissions mains are constructed of ferrous materials and are thus highly susceptible to corrosion. For many years limited consideration was given to the protection of these assets from external corrosion as it was believed that soil was a benign environment. However localised corrosion of the external pipe surface has been established as one of the main contributors to pipe bursts and leaks which disrupt potable water services leading to high associated costs. One of the primary mechanisms which cause localized pitting corrosion within potable water networks is microbiologically influenced corrosion due to the action of biofilms on the pipe surface.A novel technique for the study of microbiologically influenced corrosion in soil to further our understanding of this phenomenon on the external surface of pipelines is being developed. Microbiologically graded agar is used to simulate both the physical structure and chemical components of soil more closely than the traditionally used aqueous solutions. Solutions can be made to mimic the chemical composition of soil but this does not take into account the physical structure of soil which plays a major role in electrochemical interactions between soil steel and microbes.This paper discusses initial electrochemical tests conducted on carbon steel exposed to semi-solid agar with and without a Pseudomonas monoculture present. Two different nutrient conditions were also considered agar with low concentration sodium chloride alone and agar with low concentration sodium chloride and a commercially available yeast free nutrient broth. Both open circuit potential and potential hold experiments were conducted followed by optical microscopy and cryogenic SEM to analyse the samples.This work is part of a continuing investigation into the mechanisms of microbial corrosion at the soil-steel interface of buried potable water pipes.