Prediction of long term corrosion in soils using electrochemical tests

Previous work by the author has focused on some of the physical and practical issues of short term electrochemical testing of soils. This work has shown that electrochemical testing is valid and the results reproducible for soils. The technique can measure short-term corrosion rates and gives an insight to the different corrosion mechanisms present in an underground environment. What has not yet been well demonstrated using this electrochemical cell is whether short-term electrochemical testing relates to long-term field corrosion, particularly pitting corrosion. A successful correlation between short term corrosion testing and long-term field corrosion would give the asset owner access to a valuable predictive tool. The purpose of this paper is to critically examine the theory behind this commonly applied industry test and present some initial results of experimental testing undertaken as part of this current research. Over the past 5 years, as part of an ongoing condition assessment program, Hunter Water Australia has been collecting long-term field pipe corrosion data, and associated soil samples, for buried cast iron pipelines within the Hunter region. Various individual pipes were sandblasted and the corrosion data recorded. At each site a representative soil sample was collected for the purpose of assessment using the electrochemical test described previously (Dafter 2009). This sampling and testing program has provided an opportunity for long-term field pipe corrosion to be directly compared with short-term electrochemical tests. This paper provides a description of the short-term testing and long-term field corrosion recording that has been undertaken through this research program to date, and includes a discussion of the results of electrochemical testing that have been achieved.