 | Don't Let Premature Pipe Failure Catch You Off Guard
by Maureen Byrne, Central Bureau of Water Compliance and Enforcement |
Owners and operators of water and wastewater conveyance systems constructed of Prestressed Concrete Cylinder Pipe need to be aware of the hidden potential for catastrophic pipe failure due to prestress wire corrosion. Prestressed Concrete Cylinder Pipe (PCCP) manufactured in the late 70s and early 80s have caused major pipe failures in drinking water mains and sanitary sewers around the country. Manufacturing defects in a pipe's prestress wire causes corrosion, which greatly reduces the strength of the pipe. This corrosion makes a pipe more susceptible to bursting under pressures well below the original design strength.
One such failure occurred on March 2, 2003 in Sayreville. A 20 year old, 102 inch sanitary sewer force main owned by the Middlesex County Utilities Authority (MCUA) ruptured, flooding a nearby neighborhood and spilling over 500,000,000 gallons of sewage into the Raritan River. An extensive investigation of the failure revealed corrosion and embrittlement of the force main's prestressed wires.
To prevent future failures, MCUA conducted an inspection of the entire force main to assess structural integrity. A relatively new technology called Remote Field Eddy Current/Transformer Coupling (RFEC/TC) was used during the inspection to detect breaks in the prestressing wires. The pipeline had to be dewatered to conduct the inspection. RFEC/TC is a radio transmitter and receiver that is carried through the pipeline. The prestressing wires act as a secondary antenna. If any wire is broken, the signal is distorted. The number and location of the wire breaks can then be determined, giving an indication of pipe integrity even when there are no visible signs of trouble.
The information from the RFEC/TC investigation provided MCUA with a baseline of the pipe's condition. To continuously track the condition of the pipe, MCUA will be installing an Acoustic Monitoring System to detect new wire breaks as they occur. The system consists of hydrophone stations placed along the pipeline that monitor the pipe for acoustic events that indicate wire breaks. The number of wire breaks and their locations are then recorded. With a record of wire breaks and their locations, MCUA can identify problem areas prior to catastrophic failures.
The RFEC/TC technology provides owners and operators of Prestressed Concrete Cylinder Pipe, who have the ability to dewater their pipelines, a means to determine potential pipe failures not detected with visual inspections alone.
For more information about this innovative pipe testing technology, please Maureen Byrne at (609) 584-4200.
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