How to Improve Renewal and Re-Inspection Decision Timing for PCCP

The city of Phoenix (city) operates a 7,000-mi distribution system serving over 1.7 million people and has completed over 225 mi of prestressed concrete cylinder pipe (PCCP) inspections. Answering the need for improving rehabilitation and re-inspection timing without unnecessarily increasing risk, the city developed and piloted a method to use inspection data to extend re-inspection intervals and execute appropriately timed repair projects. The pilot study included one mile of 48- and 54-in. PCCP across a planning horizon through approximately 2050. The subject pipeline was manufactured in 1985, showed an increasing trend in structural damage across two electromagnetic inspections, and had been repaired using carbon fiber-reinforced polymer (CFRP) at a railroad crossing where differential settlement had damaged the pipe. Goals of the pilot study included: evaluate feasibility of PCCP deterioration modeling, establish risk parameters for deterioration analysis, and develop risk-based re-inspection and renewal actions and timing. Secondary factors were considered, including treatment of CFRP re-inspection requirements according to American Water Works Association (AWWA) C305 CFRP Renewal and Strengthening of Prestressed Concrete Cylinder Pipe (PCCP), and the high prevalence of wire breaks adjacent to joints on the PCCP. Uncertainty of wire break reporting near joints is an accepted limitation of electromagnetic inspection and was factored into the analysis. The analysis showed the pipeline could be managed through continued re-inspections and select pipe replacements, rather than larger-scale rehabilitation. Factoring in the city’s relatively conservative risk parameters, the analysis also justified extending re-inspection intervals from the city’s standard 10 years to 18 years for the subject pipeline.