Condition Assessment of a 66-Inch Diameter PCCP Raw Water Transmission Main

The Central Pipeline (CPL), installed in 1965, is a 66-in diameter, 12.6 mile pipeline owned and operated by the Santa Clara Valley Water District (SCVWD) in San Jose, California. Approximately half of the pipeline is constructed using prestressed concrete cylinder pipe (PCCP), embedded-cylinder type. Development in PCCP inspection technology has made it possible to detect distressed pipe with broken wires using nondestructive methods. Once distressed pipes are identified, a utility must determine whether pipe replacement, and/or pipe rehabilitation/repair, and/or continued monitoring/inspection is warranted. This paper is presented in two parts. The first part outlines the strategies used by the SCVWD to determine the appropriate course of action once distressed pipes were identified within the CPL. Spending more time up front to understand the magnitude of distress and failure risk of distressed pipe is recommended. This approach may seem costly and time consuming but it may pay off for the utility by savings on the cost of unnecessary repairs. In the second part of the paper, the results of failure risk analysis of distressed pipe in the CPL will be discussed. Failure risk analysis is based on the one hand on technology derived from finite-element analysis, hydrostatic pressure testing, and field observation of distressed pipe, and on the other hand on field inspection of properly selected sample of distressed pipe consistent with the desired reliability of the pipeline. In total, five pipe pieces were inspected using wire continuity test. All broken wires were found to have only isolated breaks related to the manufacturing process and unrelated to the corrosion of pipe or hydrogen embrittlement of wires. No repair or rehabilitation of the pipeline was necessary and there was no need for frequent inspections or monitoring.