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Technical Papers

An advanced method of condition assessment for large-diameter mortar-lined steel pipelines

This paper describes the development and application of an advanced method of condition assessment for large-diameter, cement mortar-lined steel pipelines operated by the Hetch Hetchy Water and Power Project of the San Francisco Public Utilities Commission.

The most accurate method of pipeline condition assessment is in-line inspection (ILI) using advanced nondestructive electronic methods to scan the full circumference and length of the pipeline for damage by corrosion and other causes. This technology, commonly known as ‘smart pigging’, has become relatively straightforward in unlined steel pipelines used in the oil and gas industry.

However, the presence of mortar lining in water pipelines has, until now, limited the accuracy of ILI inspection and hindered development of practical ILI methods for large diameter, mortar-lined steel pipelines.

This ILI project was conducted over a 3-year period and included development of magnetic flux leakage (MFL) tools, a caliper tool, and propulsion equipment to move the tools through the pipeline. Two full-scale field inspections using the equipment were conducted on a total of 13-miles of historic pipeline. The results were of immediate use in managing the pipeline asset.

The benefits of using this advanced method of condition assessment are compared to the traditional method using records and indirect indicators of pipeline condition.