Water Journal : Water Journal March 2011
refereed paper water MARCH 2011 103 has been used with pressures as high as 245m. The system can identify leaks in pipelines constructed of all common pipe materials, including plastic. Even leaks as low as 0.1L/minute have been detected. (b) SmartBall SmartBall (from Pure Technologies) is an acoustic sensor that rolls through the pipe. In this case, the umbilical cable is dispensed with, and the free swimming sensor saves leak noise and position data continuously onto an inbuilt digital memory card. The main application of SmartBall technology is leak detection in pressurised water mains; however, it can also be used in sewers. The ball (Figure 2), inside its protective outer foam ball (Figure 3), is inserted into the main via a tapping on the main, or through the removal of suitable fittings, such as air valves. A suitable tapping size is 100mm-150mm. The ball is inserted into a short riser and pushed down into the main using a rod with a plunger attachment. The ball is then free to travel with the flow. The ball rolls freely along the invert of the pipe propelled by the water flow, travelling at slightly less than the flow velocity. The methodology used to track the ball during its progress involves the installation of sensors on surface fittings along the main. The ball emits a distinct high-pitched sound every three seconds, which is picked up by the sensors and time stamped. The sensors are then able to track the ball as it approaches and departs their location in real time. The position of the ball within the pipeline is critical for locating the exact position of suspected leaks. Upon retrieval, data stored during the survey can be downloaded from a circuit in the ball, which includes frequency spectrums of leaks and a rotational profile. The rotational profile and the sensor tracking (ie, distance vs time of travel) enable the leak location to be determined. The extraction process consists of inserting a net into the main via a riser on a 100mm tapping. The net covers the bottom half of the pipe diameter and is controlled and secured with two fibreglass rods. A camera is also inserted into the main to observe the ball rolling into the net (in real time). The process is then reversed, with the ball being secured inside the net as it is collapsed and pulled to the surface. The operators claim 100% success in catching the ball in the net when it is deployed. Non-invasive Technologies More recently there have been developments with low-frequency sensor technology to enable manufacturers to develop point-to-point survey methods that do not require insertion of sensors into the pipe. With the latest low-frequency acoustic technology, leaks in trunk mains can be located using leak noise correlation techniques with both accelerometer and hydrophone sensors. An accelerometer sensor is connected to the pipe, valve or hydrant by a magnetic connection, while a hydrophone requires a tapping into the main to connect to the water column. Accelerometer sensors (Figure 4) detect the vibration from the leak conducted by the pipe wall, and hydrophones (Figure 5) contain a submersible noise sensor that detects the leak noise travelling through the water column. Air valves, gauging points, insertion probe flow meter installation points and water quality sample test points provide ideal locations for connecting a hydrophone (Figure 6). asset management Figure 4: Accelerometer Figure 5: Hydrophone Figure 2: SmartBall technology. Figure 3: Ball and outer foam ball. Figure 6: Tapping on the main (connection point for hydrophone).
Water Journal April 2011