Abstract
The issue of leakage within the water distribution system is one of importance not only at an economic level for the industry, but there is also a wider environmental agenda, addressing issues of water sustainability and resource management. Very little is known about the factors which lead to failure and ultimately leakage from lead-based assets encompassing both lead service pipes and lead-run joints in cast iron mains. This has led to many repairs being carried out on lead-based assets as a reactive measure, either as part of the mains renewal programme or as leaks are detected. The aim of the present project was to gain an understanding of the significant factors affecting the failure of lead pipes and joints, and the associated mechanisms of failure. To achieve this aim, a number of different research avenues were followed. A literature review was conducted investigating the influence of factors including manufacture, metallurgy and microstructure on the mechanical properties of lead. The literature review also helped to establish directions for the experimental investigations. Four key strands were developed for the experimental investigations. Firstly, a lead pipe sampling programme was conducted in order to characterise the types of failures seen in-service and their relative frequency. This showed that the most common type of failure was circumferential fractures. A microstructural study was then carried out to investigate the prevalence of microstructural defects in lead pipes, and their role in failure. This showed that a large proportion of lead pipes exhibited manufacturing defects of various types that could contribute to failure. Tensile tests were then carried out on pipe samples to investigate the influence of microstructure and age on residual tensile strength. Unlike the situation for cast iron water mains, there was no strong correlation of strength with age, suggesting that the failure of lead assets is not driven by age and therefore implying that pipes cannot be targeted based solely on age. Finally, Leakage tests were conducted on lead pipes to investigate their contribution to the overall leakage within the network. The constraining effects of the surrounding soil on the leakage from lead pipes were considered as part of these tests. These tests showed that the clay soil around the pipe played no part in limiting the leakage flow rate from any given orifice. The research avenues serve to highlight the difficulties in formulating a suitable condition assessment method for lead assets. With regard to manufacturing defects, there is a lack of data relating to the manufacturer or manufacturing method of the pipe, so pipes can not be targeted based on potential for the presence of manufacturing defects. Taken with the lack of correlation of residual strength with age, this makes targeting of replacement difficult. The work has proved valuable in steering the direction of future work and given an insight in to how future rehabilitation or replacement of lead pipes within the water industry may be approached.