Asset Management of Asbestos Cement Pipes Using Acoustic Methods: Theory and Case Studies

Asbestos cement (AC) water mains were installed in the United States and Canada, from approximately 1940 to the early 1980's. According to the American Water Works Association, approximately 18% of the installed mains are AC, while EPA (2000) estimated a somewhat lower number at 15% of the total mains in the United States. While much of the installed AC pipe is in excellent condition, it has been noted by utilities that operate this type of pipe that some areas are prone to degradation. As the pipe ages, it is also noted that burst rates can begin to increase in frequency (Hu and Hubble, 2007). Condition assessment of Asbestos Cement pipes has been problematic for many utilities. Currently, the primary method used is to dig to the pipe and extract physical samples for testing of physical properties. Due to the cost, and problems with the statistical significance of thus method, few utilities have a full picture of the condition of their asbestos cement assets. The acoustical method relies on measuring how quickly an acoustical signal is transmitted along a section of pipe, using easy-to-access measurement locations such as fire hydrants and control valves. Changes to the signal-specifically changes to its transmission or propagation velocity-can be related to changes in the pipe wall stiffness. Echologics has recently undertaken extensive implementation and testing of the technology on asbestos cement pipes with Las Vegas Valley Water District. Studies and testing have also been performed in Richmond BC, Ottawa ON, and Tacoma WA. This paper will describe an acoustical method to determine the remaining structural wall stiffness of asbestos cement pipes. A review of the asset management procedures being used for AC pipes in Las Vegas will also be presented. This paper will outline several factors regarding the need for AC pipe assessment, including current EPA and California standards for asbestos