So Now What? Tough Decisions When Monitoring a PCCP Transmission Main

Electromagnetic inspection followed by acoustic fiber optic (AFO) monitoring is a strategy used by many utilities to manage prestressed concrete cylinder pipe (PCCP) transmission mains. The electromagnetic inspection obtains a baseline condition of the prestressing wire wraps while the AFO monitoring detects each subsequent wire break. This data can be coupled with structural analyses for an up-to-date condition assessment of each section of pipe. However, translating the condition assessment to actionable information is not always straightforward. A number of factors, such as the rate of wire breaks, pipeline history, hydraulic concerns, criticality, consequence of failure, and other work being completed at the time all need to be considered. This paper highlights three unique case studies regarding AFO monitoring decisions for one utility. Each case study discusses an active PCCP that experiences a number of wire breaks, as detected by the AFO monitoring system, and the factors and elements that led to the subsequent decision to repair the pipe section or to continue to monitor. The paper shares lessons learned and experiences from engineers that are challenged with the task of managing PCCP on a daily basis.