Listening for Leaks
Acoustic Technology Helps German Water Utility Assess Asset Health and Predict Network Failures.
Echologics ePulse Acoustic Technology
Known for their well-functioning drinking water distribution network, German water suppliers invest around EUR 1.5 billion annually on infrastructure maintenance. Most utilities have a portion of aging pipes and unsustainable supply networks, as is the case with Netzgesellschaft Düsseldorf mbH (NGD). Faced with infrastructure reaching its end of life, it became critical for the utility to find a way to anticipate failures, so that they could prioritise maintenance and keep up with daily operations, while managing the necessary capital expenditures.
NGD, a wholly owned subsidiary of Stadtwerke Düsseldorf AG, is responsible for network operation for the North Rhine-Westphalia capital of Düsseldorf in the area of energy and water supply. They provide the infrastructure for the distribution of electricity, gas, water and district heating to more than 600,000 residents, with a water pipe system that extends over 1,700 km.
NGD identified a significant amount of transmission and distribution mains made of steel and cast iron that were installed between 1950 and 1965. These pipes were said to be strongly prone to corrosion. Due to the absence of historical data and limited capacity of underground work to assess its structural condition and remaining service life, NGD searched a cost-effective solution to prioritise its pipeline rehabilitation and replacement decisions. The utility’s asset management team turned to Echologics® ePulse ®condition assessment technology from Mueller Water Products.
“We chose the ePulse because of its unmatched ability to locate leaks non-invasively while assessing factual pipe condition versus theoretical,” said NGD Asset Manager, Markus Wall. NGD and Echologics field crews collaboratively selected a 35km section, critical to the city’s supply network to kickstart the project.
ePulse technology can assess the condition of distribution and transmission mains, while simultaneously searching for leaks without the need for large excavations or service disruptions.
This is accomplished by attaching acoustic sensors to existing contact points, such as fire hydrants, valves or direct contact with a pipe. A sound wave is then induced in the pipeline and travels along the pipe. The acoustic sensors capture the time it takes the sound wave to travel between two sensor stations. The speed at which the sound wave travels is dictated by the condition of the pipe wall.
As the sound wave travels, it pushes water molecules toward each other. Because water is incompressible, the molecules push outward on the pipe wall. This places a microscopic flex on the pipe wall — and greater the flex, the weaker the pipe. Through this acoustic technology it’s possible to measure the actual strength of the pipe wall which is an ideal measure of actual pipe condition.
These results supported NGD’s cast iron replacement decisions by rapidly assessing the structural condition across the pipe network to prioritise areas with the worst degradation for immediate pipe replacement.
Positive correlation 33.5m from the white sensor, within the test section
For the steel pipe sections, broadband electromagnetic measurements (BEM) was also used to characterise the pitting distribution on each section of pipe. Pipe measurements and other pipe condition datasets were then paired with a structural analysis to determine the condition of each pipe.
Cast iron trunk main selection: ePulse condition assessment
A total of 27.7km section was assessed using ePulse technology with three leaks successfully pinpointed. Below is a summary of decisions made by NGD, considering Echologics’ experience
Steel trunk main selection: ePulse condition assessment and BEM
900m of DN600 and 500m of DN1200 Steel mains were assessed using ePulse technology. Below is a summary of findings:
The minimal average remaining structural wall thickness calculation aligned with the pitting distribution and the minimal wall thickness values gathered through the BEM measurements, provided a useful dataset for NGD to make informed replacement decisions.
“At NGD, we seek resilient water systems to anticipate and monitor changes to pipe condition. The data-driven insights we gathered from ePulse have not only helped us safeguard the long-term availability of clean water for all customers and stakeholders in this city, but also efficiently allocate operational resources,” concluded Mr. Wall.
Netzgesellschaft Düsseldorf mBH plans to re-measure the moderate pipes with ePulse technology after five years to evaluate the change in structural remaining wall thickness.
Site plan #2 indicating the pipe segments surveyed, which are color coded in three categories: green (good), yellow (moderate), red (poor).
Author: Mark Nichol
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