Assessing and Managing PCCP Water Transmission Mains, Baltimore County, Maryland — A Case Study

Prestressed concrete cylinder pipe (PCCP) often plays an important role in the transmission systems for medium to large utilities. Although PCCP has been a very durable product, a number of sudden catastrophic PCCP failures have occurred throughout the U.S., most of which have stemmed from corrosion and subsequent failure of "Class IV" prestressing wire. Baltimore County, Maryland has implemented a state-of-the-art assessment and management program for a 48-inch PCCP transmission main which feeds water from a major pumping station to a large finished water reservoir. The program consisted of two phases — electromagnetic testing simultaneously with visual inspections for Phase 1 and acoustic monitoring for Phase 2. As a result of the Phase 1 inspections, four pipe sections were identified as requiring immediate replacement before the main could be returned to service. Subsequently, the four pipe sections were dissected as a part of forensic analysis. The actual number of wires broken were compared with those previously predicted using the electromagnetic inspection techniques. The Phase 2 assessment program was modified to incorporate new technology which used "fiber optics" in addition to the planned "acoustic" technology to monitor on-going wire breakage over a 90-day period.