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Baltimore County Now

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Date: Jul 26, 2013

image of the inside of a sewage pipelineJohn Van Ness
Associate Engineer, Baltimore County Bureau of Utilities

How do you inspect more than 60 miles of pressurized sewer pipelines when they are all underground and must continue operating during the inspection? As with so many issues in our modern world, we turn to technology.

Baltimore County Bureau of Utilities operates more than a hundred Sewage Pump Stations, each with at least one pressurized pipe (called a force main) to transfer sewage to a gravity sewer main or another pump station, eventually ending up at a either the Back River or Patapsco wastewater treatment plants. The total combined length of pump station force mains is 62 miles and the longest of them are over 3 miles in length. Inspecting these force mains is a challenge because there is no access along the length of the pipe, only at either end. In addition, they must remain in operation and they are typically buried underground where they cannot be observed. With advanced technology Baltimore County is inspecting these mains while they remain in operation and learning more about potential problems that cannot be seen with the naked eye. 

The Pure Technologies PipeDiver inspection tool is a 15-foot long, 3-sectioned submarine that uses electromagnetic instruments to determine overall pipe strength and can identify any problem areas to within several feet. We were the first agency to ever use this free-swimming tool that is put in the pipe at the station while the station is operating and is caught at the other end in a specially constructed cage in the gravity manhole. With what is learned from the PipeDiver we can make educated decisions on whether to replace a force main, repair it or re-inspect at a later date.

The SmartBall tool, also from Pure Technologies, uses sound recording and advanced location technology to find leaks and air pockets in force mains. A leak is an obvious problem but air pockets will trap corrosive gases that will corrode and weaken pipe unseen on the outer surface of the pipe. The SmartBall comes in sizes from 4 inches to 7 inches and like its name, it looks like a blue foam toy “Nerf” ball. The ball is put in the force main at the station and rolls along the pipe counting rotations and recording the specific sound signatures that indicate a leak or air pocket. It is caught much the same way as the pipe diver but often a crab or fish net is used just as effectively as a cage.

When the station has enough capacity or the force main is short enough that we can turn off the pumps to do an inspection we can use robotic tools to inspect pipe as well. These will have a combination of the above technology in addition to a closed-circuit TV camera. The largest one we have used is 6 feet long, weighs 300 pounds and looks like a miniature tank complete with two sets of tracks and an articulated camera.

Replacing force mains is expensive, and the use of advanced technology is allowing the County to reduce maintenance costs by only replacing those portions of pipe that need replacing and taking action before breaks might occur.


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