Case Study in Morocco: Leak Detection on Large Diameter Transmission Mains
Background Issue
Transmission water mains are large diameter pipelines that carry water from a source or treatment plant to the distribution system, serving as the main artery of a water supply network. Transmission mains are designed to transport large volumes of water over long distances, usually through rural or back country areas. They are typically larger in diameter than distribution mains, often exceeding 24 inches or 600 mm.
Transmission mains are generally installed with limited connections, ensuring system reliability. These pipelines often operate at lower pressure than the distribution system, 2 – 3 bar (30 – 45 psi) as opposed to 4 – 5 bar (60 – 75 psi). The lower pressure, along with the low number of listening points, makes identifying and pinpointing leaks using Continuous Correlating Acoustic Monitoring (CCAM) systems difficult.
The low pressure reduces the sound generated by leaking pipes and the larger spacing of acoustic sensors limits the ability of the monitors to accurately detect and correlate the leak location. Regular inspection and maintenance of these large capacity water mains אני are vital for avoiding disruptions, quality issues, or large-scale failures.
Distribution pipe failure rates are six times that of transmission lines, but large diameter transmission line failures have a more serious impact on the delivery of water to customers. They are singular assets serving a large population with no backup. Monitoring these pipelines is critical to ensure reliable delivery of water to the entire customer base.
Conventional Leak Detection Methods
There are many options for finding leaks on water distribution mains. These include handheld acoustic devices, software-based condition assessment solutions, District Metered Areas (DMA’s), floating sensors and CCAM systems. Most of these approaches cannot be adequately applied to transmission mains due to their unique qualities. Large diameter transmission mains typically operate at low to medium pressure and have very few access points for monitoring. This is where AQS Systems technology separates itself from the other options in the marketplace. The AQS propriety sensor technology and analysis algorithm allow the system to detect more leak sounds at a lower installation density. This means AQS can find leaks where other systems cannot.
Goal of Project
A major utility in Morocco oversees water distribution, sewage management, and the reuse of treated wastewater for one of the country’s key urban centers, serving 500,000 inhabitants. To enhance the short-term performance of its water infrastructure, the utility implemented a smart monitoring system designed to precisely identify and locate leaks within the network. This initiative also aims to rationalize operating costs, optimize expenses related to leak detection, and improve the responsiveness of repair teams. Additionally, the system provides critical data to inform decisions on potential rehabilitation interventions.
AQS System design and Results
This utility implemented a continuous acoustic monitoring system for the DN600 transmission main, a 600mm (24 inch) prestressed concrete pipe that runs approximately 7.5 km (4.7 miles) with operating pressures under 3.4 bar (50 psi), connecting a 10,000 m3 tank to a nearby pumping station.
The water utility chose AQS smart acoustic hydrophones correlators for this project. A total of 24 hydrophones were installed on the 7.5 km pipeline, 20 in underground chambers on automatic air valves and 4 on underground control valves. The sensors’ audio sampling data is automatically backhauled to a cloud platform for analysis via a 4G cellular network.
Hydrophones were installed at intervals of up to 540 meters (1800 feet) apart.
After 4 days of monitoring several leak alerts were generated.
One of the leaks identified and fixed was correlated with a distance of 290 meters (950 feet) between the sensors. As can be seen from the leak sensor intensity graphs, the leak sensors were able to detect the leaks from either side. Leak sensor 72114 was 245 meters from the correlated leak location and Leak Sensor 72133 was 45 meters from the location. The leak noise intensity was lower overall at sensor 2, but it is clear that both sensors recorded baseline sound levels when the leak was repaired and were also able to overcome the interference in the noise generated by the pumping station at the extremity of the pipe.
The second alert identified a leak between two sensors spaced 210 meters (690 feet) apart. This alert was confirmed in the same manner. At first, this alert appeared not to be a water leak, but a high-intensity sound created inside the pipe at the location indicated, possibly due to a nearby throttling valve creating an obstruction and hampering the regular flow of water. However, further investigation along the pipe found a large water leak a few meters away from the alert, between the sensor and the AQS correlator.
The two noise graphs show distinct peaks at various times during the data collection period, and show a steep drop off after the leak is repaired. This ability to correlate leaks from distance and on low pressure pipe is a hallmark of the AQS system. Another alert worthy of note correlated a leak where the distance between the sensors was 395 meters (1300 feet).
The alert was confirmed using manual correlating equipment and excavation of the area confirmed a large water leak at the junction of the water main and the concrete infrastructure of the valve chamber.
It is important to note that a second leak was found in the same area after the repair. Its sound was concealed by the more intense acoustic signal from the first leak. Subsequent to the first leak being fixed, the sound from the second leak became more pronounced and was able to be pinpointed and correlated and ultimately repaired.
Additionally, a third alert came up within 15 meters from this position, and the operator is now in the process of investigating it.
This enforces the idea that a continuous acoustic detection system should be deployed as opposed to performing periodic surveys. The continuous nature of the AQS system allows for leaks to be identified as soon as they exhibit a noticeable acoustic signal, and the leak can be tracked until it is clearly pinpointed and scheduled for repair.
A total of five leaks have been found, pinpointed, and repaired since the implementation of this program. This reinforces the value of the AQS continuous sensing system and that there may be many more leaks on transmission lines than previously believed.
The customer was very satisfied with the results from the AQS system and the technical support, saying “We would have not found these leaks without the AQS system. The water savings is very significant and our ability to manage the asset has greatly increased our system reliability and resiliency.”
Summary and Conclusions
It is estimated that these five leaks contributed to a 10,000 cubic meters per month (1 million gallons per day) water loss. An additional 8 alerts have been generated but have not yet been inspected.
The use of extremely sensitive hydrophones can detect acoustic signatures of leaks and other in-pipe disturbances on large diameter transmission mains where there are large distances between sensor points.
Continuous correlating acoustic leak detection systems are able to quickly identify leaks, minimizing water loss and preventing major failures more efficiently than periodic inspections.