Condition Assessment of In-Service Ferous Mains

Most of North America's oldest water mains are constructed of ferrous material, in particular cast iron, ductile iron, and steel. Budgetary realities often make it impossible for utilities to replace these pipelines at the end of their design life. Utilities are increasingly looking to asset management programs to help direct scarce resources to where they are most needed, and these programs depend on reliable condition assessment information. There is an obvious need for condition assessment tools that will allow utilities to implement selective repair and replacement strategies based on the actual condition of their pipelines. In order to keep the overall project cost and effort manageable, and to maintain customer service levels, these technologies need to be able to address pipelines while they are in service. This paper outlines two approaches that are now available for condition assessment of metallic mains while they remain in service. The first is a tethered inline inspection system which can detect discontinuities in the pipe wall, internal corrosion, damage to or loss of the liner, and has now been adapted to provide indications of average wall thickness over set intervals. The second is a new free-swimming "smart pig" allowing for Remote Field Eddy Current (RFEC) testing of metallic pipelines, which provides detailed readings of metal loss, even through a pipe liner. Technology specifications and case studies are presented for both approaches. An approach to using this information to estimate remain life of pipelines is also discussed.