City to Inspect Southwest Transmission Main

City to Inspect Southwest Transmission Main

Baltimore City Department of Public Works Director Alfred H. Foxx today announced the beginning of a comprehensive evaluation of some of our larger and more vulnerable water mains using state-of-the art technology. Beginning Tuesday, DPW will conduct an inspection of the 60 and 54-inch Southwest Transmission main. The serves as the primary conduit for distribution of water from the Ashburton Water Treatment Plant to portions of Baltimore City, Baltimore County, Howard County and Anne Arundel County.

Many of the larger water mains in the Baltimore Metropolitan Area are manufactured pre-stressed concrete cylinder pipes or PCCP. As the name implies, these consist of concrete with a steel cylinder for waterproofing and are reinforced with high tensile steel wire which is applied to the pipe under tension thereby pre-stressing the concrete. The attached diagram indicates the components for pipe manufacture.
Baltimore City has approximately 110 miles of PCCP in the water system ranging from 30-inches to 144-inches in diameter. During the mid-1970’s this type of pipe (Class 4) was manufactured using high tensile wire that was affected by moisture in a process called hydrogen embrittlement, resulting in the wires losing their strength and premature failure. This is what occurred at various locations with major pipe failures, including Dundalk and Halethorpe in 2009. Just under 20% of the 110 miles is of this Class 4 type.
Baltimore City and our neighbors are aware of this problem and that is why we are taking steps to identify all the PCCP mains with the manufactured defect. The City has embarked on a program to identify which mains are most at risk, making these subject to failure. The attached map shows these mains. The ones already inspected are highlighted in yellow.
The City has conducted a number of investigations of these mains and will be looking at the remaining ones over the next 5 years. This work involves identification of broken wires and the City has taken steps to repair or replace the distressed pipe sections and will continue to evaluate and prioritize mains based on the inspections.
In the past the evaluation of these pipes required taking them out of service. This would enable workers to enter and conduct a physical and electromagnetic inspection to identify which sections contained broken wires. The technology to conduct this work has advanced to the extent that the Southwest Main inspection will be conducted with an enhanced tool, which is a free swimming Pipe Diver ® that is launched into the inside of the pipe at an access point and retrieved at a point downstream. It relies on the flow in the pipe to propel the inspection tool forward while electromagnetic waves energize the wrapping wires and determine where wires have broken. A picture of the Pipe Diver ® is attached.
The inspection of the Southwest Transmission Main will be the first time that Baltimore has deployed this free swimming tool to inspect a water main under pressure, without affecting service to customers. When deployed, the pipe diver is approximately 12 x 6 feet and has the appearance of a large fishing lure. It will be retrieved using what is essentially a small submarine.
The Southwest Transmission Main to be inspected commences in Leakin Park near Morris Road and the end of the inspection is approximately 6 miles away (30,000 feet), near Monumental Avenue in Baltimore County, where the main splits with service going to Howard and Anne Arundel Counties.
Consumers should not even become aware that the inspection is being conducted. There is a very low probability that the inspection tool could become lodged in one of the system valves, in which case the main will have to be temporarily shut down to allow for access and retrieval of the Pipe Diver ®. The map provides details of the approximate location of the main to be inspected.
After the main is inspected the results will determine which, if any, sections of the pipe need repair or replacement. In order to repair a main it must be taken out of service. The pipe is then re-lined with either steel or a carbon fiber coating to restore the pipe’s required strength. The schedule for these repairs will be set based on the severity of each main.
When: Tuesday, March 6, 2012
Time: To see the Pipe Diver ® before deployment, media are asked to be on-site at 3:30 P.M. Deployment will actually occur around 9:00 P.M. with a recovery around 8:30 A.M. the next morning.
Location: Morris Road 100 feet south of the intersection of Winterbourne Road in Leakin Park.
For video showing this technology please visit: http://www.puretechnologiesltd.com/