Bringing Multiple Assessment Methods to Bear to Manage a 1970s PCCP Transmission Main Susceptible to Continuing Wire Breakage

As part of an ongoing comprehensive condition assessment program undertaken by the City of Mesa (COM), Arizona, two 42 in. diameter prestressed concrete cylinder pipes (PCCPs) manufactured in the mid-1970s were excavated for external inspection to verify the results of electromagnetic (EM) inspections performed 2 years ago and update the failure risk and repair priorities of distressed pipes along the pipeline. Inspection of the two pipes revealed brittle wire breakage and discrepancies between the EM-predicted and actual number of broken wires, which led to a detailed investigation to determine the root causes of degradation, evaluate risk, and plan for future actions to maintain pipeline reliability. The investigation included external inspection of all eight previously identified distressed pipes; teardown inspection of one that was selected for replacement; petrographic analysis and laboratory testing of mortar coating quality and condition; mechanical testing of prestressing wires and steel cylinder; and soil corrosivity. This paper demonstrates comprehensive assessment of PCCP using multiple inspection, testing, and analysis methods, including presenting the purpose and results of each component of the investigation as well as synthesis of all results to develop recommendations for future actions to manage the pipeline for continued reliable operation.