Evaluation of Relining Options for a 6-mile, 144-inch Steel Pipeline

The Etiwanda Pipeline is a 144-inch diamete,r welded steel pipe, approximately 6.4 miles long connecting the Metropolitan's Rialto Pipeline to the Upper Feeder. The pipeline, constructed in 1993, has dual functions: an untreated water transmission pipeline and a penstock supplying water to the 24 MW Etiwanda Hydroelectric Plant. The pipeline experiences significant daily pressure fluctuations as flows change to optimize power plant revenue. A 2008 inspection revealed that over 35 percent of the field applied cement mortar internal lining had fallen off or had become delaminated. The unique operating conditions, the large diameter of the pipeline, the length and limited access opening for repairs and, in particular, the dual purpose of the pipeline presented unique challenges to replacement of the lining. There are few, if any, precedents for this type of pipeline, which makes the selection of the replacement lining very challenging. This paper will describe the approach adopted to evaluate potential lining repair alternatives in order to select the most cost-effective and constructible lining. The paper will review the life cycle costs of various lining systems, and provide a history of similar flexible lining repairs. The repair technique ultimately selected was complete removal of the mortar lining and installation of a flexible lining system over the entire length of the pipeline. This lining system should provide the desired 50-year service life.