Long-term corrosion of cast iron cement lined pipes

SUMMARY: The corrosion of ferrous water mains is a signific ant problem for the Australian Water Industry. A significant proportion of Australia’s a geing water infrastructure is composed of cast iron and steel cement lined pipes, which are prone to co rrosion on the external surfaces that are in contac t with soil. Internal corrosion is not a significant issue for cement-lined pipes. For the water industr y to manage these ageing assets effectively, quantitativ e predictions of the damage likely to result from long-term corrosion are highly desirable. Many of t he fundamental corrosion mechanisms are known and there is considerable practical experience on t he corrosion of buried iron. However, the predictio n of the long-term corrosion losses, of pit depths an d pitting extent are not well developed, including understanding and prediction of the quantitative in fluences of external soil conditions. In this paper the basic mechanisms involved in the corrosion of ferro us metals in contact with soil are reviewed and the likely effects of various influencing factors such as soil moisture content, soil type and soil water chemistry on long-term corrosion are described. The review has found that long-term corrosion is controlled by diffusion processes and is a function of soil moisture content, soil density, and soil w ater quality. The review is followed by an outline of an approach to modelling long-term corrosion of cast iron pipes. It involves developing a realistic mode l for the prediction of pipe corrosion in soil and its calibration to field and historical data. Both the modelling approach and field data collection requirements are outlined.