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

摘要

Eight breaks have occurred on a 16-inch diameter recycled water transmissionrnpipeline, most recently in October 2008. After a break in September 2006, becausernthe pipeline is only about 12 years old, an investigation was structured to determine ifrnthere is a systematic problem. Two of the most recent breaks occurred less than 100rnfeet apart, in Kanan Road, near its intersection with Hawthorne Drive, in the OakrnPark area of Ventura County, California. The five most recent failures-in 1999,rn2003, 2006, 2007, and 2008-necessitated round-the-clock emergency repairs withrnthe associated impacts to traffic and the public.rnThe pipeline was constructed of PVC that was specified as conforming to AWWArnStandard C905. Pipe manufactured to that standard has a nominal design safety factorrnof 2.0 at 100,000 hours (11.4 years) of service at its rated pressure. This particularrnpipe is DR-25, which is rated for 165 pounds per square inch (psi) (without surge),rnand the static pressure is approximately 140 psi at the most recent point of failure.rnThis paper describes the investigation into the possible causes of failure,rnincluding conducting laboratory tests, surge analyses, and design replication. The riskrnto continued operation of the pipeline (expecting to have further breaks) wasrnaddressed along with repair and replacement as means of addressing the continuedrnlongevity of the pipeline.