This sound wave reverberates all along the pipe

Water becoming a valuable asset and rare, it is imperative to the spoil. The companies responsible for the management of water distribution networks now put in place systems to detect leaks. This is the case of Lyonnaise des Eaux, which has implemented a new system in Dijon. It must be said that in France the performance of the network is low, the order of 76. This means that a quarter of the water made available to the network is never to tap consumer, lost on the road because of leaks. Or locate these leaks is not easy. The problem is to analyze permanently dozens, even hundreds of kilometres of pipes.

Piezoelectric sensor

Traditionally, known to locate the leak using acoustic sensors. Moving under pressure in a pipeline, water escapes in the open air relaxes and generates a particular noise. This sound wave reverberates all along the pipe. Much like an ear on the pipeline, a sensor placed on a valve head, accessible from the road with a small round trap, means everything that is happening within a radius of several hundred metres. These sensors are installed on a temporary basis and then recovered so that their data are analyzed by computer.

The German company Sewerin GmbH, specialist for the detection of leaks of gas or water networks, had the idea of "listening to" pipe permanently through GSM telephone communications. Lyonnaise des Eaux completes the installation of this system on the 525kilomètres of network of the city of Dijon. Its major competitor, Veolia Environnement, has done the same, less large scale, Troyes and Saint-Dizier.

The pilot project of Dijon uses German detection technique combining acoustic detection and transmission GSM. In the device installed on the line, a piezoelectric accelerometer measure all the vibrations within a RADIUS between 20 hertz (Hz) and 2,000 Hz, frequencies in approximately 200 metres. The enemy is the parasitic noise. The electronic apparatus therefore knows eliminate alone the vibrations of a frequency of 50 Hz, which are those of electrical installations, such as refrigeration systems. Another precaution, the registration was held that night, for 30 minutes, between 3 and 4 hours of the morning, the time at which the water system is little used, so silent.

The sensor performs a record per second. Then an electronic system eliminates all noise peaks: truck, flow suddenly in the pipeline... "What we are concerned, it is persistent and stable minimum noise." "The one that reveals a leak", said Antoine Lecuona, head of Agency of Lyonnaise des Eaux in Dijon. This residual noise is characterized by an index, that is sent to the central system by a GSM Transmitter specially developed by Sewerin. At Dijon, Lyonnaise des Eaux and installed permanently 165 sensors to inform the functioning of the network on a daily basis.

Real time analysis

Remains then to refine the stalking of leaks. A work which is done by correlation. It is indeed likely that a leak is detected by several sensors. For each of them, the intensity of the recorded signal because of the importance of this leak, but also depends on the distance at which it lies and, finally, in some cases, the type of pipeline. "Those PVC or polyethylene, more flexible, absorb vibration benefits than cast iron mains.". "Noise is the same, but occasionally filtered", says Maxime Kieffer, the French subsidiary of Sewerin.

At Dijon, with this project in 280,000 euros, the company that shows 81 yield, and hopes to reach 85. "Because we have an almost real-time network behaviour analysis." Previously, by a prélocalisation neighbourhood by neighbourhood, needed us an average 180 days to locate a leak. "Today, a few days suffice", insists Antoine Lecuona.