Looking beyond Broken Wires: Baltimore’s Approach to PCCP Condition Assessment

Prestressed concrete cylinder pipe (PCCP) is a composite pipe that combines the compressive strength of concrete, the watertightness of the steel cylinder, and the tensile strength of pre-stressing wires. Because of their use in large-diameter transmission mains and corresponding consequence of failure, mitigating failure risk through proactive condition assessment and pipe rehabilitation have largely been adopted by the industry as a best management practice. PCCP failure can be multifaceted; while the most traditional approach to PCCP condition assessment has focused on quantifying broken wire wraps to model the state of pipes, Baltimore has observed multiple distressed pipes with no corresponding broken wire wraps. Forms of distress observed correspond to longitudinal failure due to uneven settling of bedding material due to poor installation, overlap of underground assets, and transition from encasements. Baltimore’s experience illustrates the importance of combining inspection methodologies for a more holistic condition assessment approach, where leak detection and visual and sounding inspections should be complemented with electromagnetic surveys to identify all pipes with an unacceptable high risk of failure. Best management practices for prevention of these failure modes as well as appropriate rehabilitation option are also discussed.