Overnight Tuesday, a wormlike apparatus with green plastic tentacles sending out electromagnetic waves was to wind its way through nearly six miles of a Baltimore water main, detecting potential trouble areas along the pipe.
"This is better for pipes that can't be taken out of service" for manual checks, said Travis Wagner, a civil engineer with Pure Technologies, a company with offices in Columbia that owns the tool, called the PipeDiver.
The device is being used to inspect the Southwest Transmission Main, a stretch of pipe that is more than four feet in diameter and runs from the Ashburton Water Filtration Plant in Northwest Baltimore into Baltimore, Howard and Anne Arundel counties.
It's the first inspection of this type in Baltimore and is expected to accomplish in less than 12 hours what would normally take at least two weeks. Moreover, the PipeDiver is expected to cost less and reduce service disruptions. It's difficult to estimate the full cost of manual inspection, city officials said.
The Southwest Main is made up of pipes — called pre-stressed concrete cylinders — that have a layer of wire wrapped around a concrete-and-steel core. Over time, the wire can degrade and break, making the main more likely to burst.
Tuesday night's inspection was intended to prevent ruptures like the one in September 2009 that flooded dozens of Dundalk homes. A 6-foot-wide pre-stressed concrete main released millions of gallons, deluging a shopping center and washing out a main southeast Baltimore County road.
Kurt Kocher, a spokesman for the city's Public Works Department, said that crews began preparing the pipe around noon Tuesday by draining water from several feet of the main where the device was to be inserted.
The PipeDiver was scheduled to be released at 9 p.m. It was to travel along with the water's current until it is ready for retrieval about 5.7 miles downstream at 8:30 a.m. Wednesday.
Pure Technologies will analyze the data collected in Tuesday evening's inspection and notify the city of problem areas along the main in about two months, Wagner said.
Traditionally, pre-stressed concrete cylinder pipes have to be emptied of their water and inspected manually.
"The time, de-watering costs are astronomically high" and inconvenience a lot of residents and businesses, said Graeme Lake, an associate with Patton Harris Rust and Associates, an engineering firm that the city has hired as a consultant for the Southwest Transmission inspection project.
The Southwest Transmission Main is an ideal candidate for using the PipeDiver because the backup options for providing water are limited or nonexistent. The cost to inspect and analyze the Southwest Transmission Main is about $800,000, Lake said.
The PipeDiver has been in use for about three years, Wagner said, and has already been deployed in several U.S. and Canadian cities, including Dallas and Louisville, Ky. In July, Baltimore County used the PipeDiver to inspect a pre-stressed concrete wastewater main.
"There's a slight chance where it could get stuck near a valve" creating a temporary service interruption, Kocher said.
That's why the apparatus was deployed overnight, when demand for water is less, said Michael Marquis, a city engineer.
The Department of Public Works anticipates using the PipeDiver on other pre-stressed concrete mains, including a main in Northeast Baltimore from the Montebello Water Filtration plant that is more than seven feet in diameter. Inspection of that main is scheduled for next year.