From Planning to Inspection to Emergency Repair of a Large Diameter Pipeline

The Middlesex Water Company (MWCo) owns and operates two parallel pipelines that convey up to 60 million gallons per day (MGD) of raw water between their raw water pumping station located in the city of New Brunswick, New Jersey (NJ), and their Carl J. Olsen Water Treatment Plant (CJO WTP) located in the township of Edison (Edison), NJ. One of these pipelines is a 5,200 linear foot (LF) 54-in. prestressed concrete cylinder pipe (PCCP) installed in 1969, and the other is a 6,250 LF, 60-in. ductile iron pipe (DIP) installed in 2005. Although there had been no known issues with the 54-in. raw water supply main throughout its 52 years of service life, MWCo recognized the importance of inspecting this critical pipeline to determine its current condition and ability to reliably convey raw water to its treatment plant. In order to assure its long-term integrity and viability to supply MWCo’s treatment plant serving approximately 450,000 residents in eastern Middlesex and northern Monmouth Counties, MWCo undertook a condition assessment of the 54-in. PCCP pipeline in early 2021. This condition assessment consisted of a manned internal inspection involving wall sounding, and visual and electromagnetic assessments. The electromagnetic inspection determined that a number of pipes had broken prestressing wires, which necessitated the need to perform a finite element analysis. This analysis determined the yield limit for failure of the PCCP pipe class used in the construction of the pipeline. The visual inspection found a number of pipes with circumferential/longitudinal cracking, hollow-sounding areas, and delamination of the inner core. Additionally, one (1) pipe was found to have a circumferential failure within the pipe barrel, which was allowing water to actively infiltrate into the pipe. As a result of this, MWCo undertook an emergency repair, which involved the installation of an internal carbon fiber reinforced polymer (CFRP) system. Additional intrusive investigations were performed on various pipes with observed and detected damage in order to determine the need for additional repair and to determine the reason for damage. MWCo also utilized this inspection as an opportunity to perform an inertial mapping survey of the pipeline in order to better understand how the actual horizontal and vertical alignment of this critical pipeline compared to the original design and construction documents. This paper will discuss the need for the inspection and planning efforts that were undertaken by MWCo as well as the types and results of the inspections performed as well as the emergency repair work.