Several Failures of a 16-Inch PVC Transmission Main within 12 Years

Eight breaks have occurred on a 16-inch diameter recycled water transmission pipeline, most recently in October 2008. After a break in September 2006, because the pipeline is only about 12 years old, an investigation was structured to determine if there is a systematic problem. Two of the most recent breaks occurred less than 100 feet apart, in Kanan Road, near its intersection with Hawthorne Drive, in the Oak Park area of Ventura County, California. The five most recent failures—in 1999, 2003, 2006, 2007, and 2008—necessitated round-the-clock emergency repairs with the associated impacts to traffic and the public. The pipeline was constructed of PVC that was specified as conforming to AWWA Standard C905. Pipe manufactured to that standard has a nominal design safety factor of 2.0 at 100,000 hours (11.4 years) of service at its rated pressure. This particular pipe is DR-25, which is rated for 165 pounds per square inch (psi) (without surge), and the static pressure is approximately 140 psi at the most recent point of failure. This paper describes the investigation into the possible causes of failure, including conducting laboratory tests, surge analyses, and design replication. The risk to continued operation of the pipeline (expecting to have further breaks) was addressed along with repair and replacement as means of addressing the continued longevity of the pipeline.