The utility has been installing acoustic equipment inside its largest water mains to detect the onset of any snapping of the steel wires that reinforce the concrete. The snapping is a sign that the pipe is failing; the monitoring is designed to make it possible to replace affected portions of the pressurized pipe before a potentially catastrophic blowout.
This is at least the third time in the past several years that acoustic equipment installed in a pipe has alerted WSSC to a potential break, allowing for a preemptive shutdown.
One such shutdown occurred in the Rockville area this spring, utility officials have said. In 2010, water restrictions were imposed over the Fourth of July weekend after a 96-inch pipe was shut down in Potomac.
At least two forms of prestressed pipe have been manufactured. In both, the wire is wrapped around the pipe. In the older form, the wire is wrapped around a steel cylinder, which in turn covers a concrete core. In the more recent form, the wire is wrapped directly around the concrete core. The wire is used to produce compression to offset stresses in the pipe.
The utility is still reviewing the March break of a 60-inch pipe in Chevy Chase, where the force of the blast blew a crater 20 feet deep in a side street off Connecticut Avenue, creating a 40-foot-high geyser. In that case, utility officials said, no warning was received because the break occurred near a joint where there was no wire or monitoring.
The main that triggered the latest alarms is inside the Beltway between Suitland Parkway and Forestville Road. The WSSC said it is in a relatively inaccessible spot, and officials said a road was being constructed Monday night to bring in repair equipment.
Irvine said that repair equipment should be on site sometime Tuesday morning and that the main will be taken out of service. Another WSSC official said the replacement could begin as soon as Tuesday afternoon.
Once the main is out of service, authorities said, the only water available in the system would be in the storage facilities and whatever remained in the portion of the pipeline downstream of the replacement area.
The WSSC’s 350 miles of prestressed concrete cylinder pipe form the backbone of its distribution system for 1.8 million people in Montgomery’s and Prince George’s counties.
Katie Shaver contributed to this report