Dual benefits of new generation noise loggers

Water companies are making significant cost savings as well as dramatically improving their identification and rehabilitation of water leakages with intelligent acoustic noise logggers.

Fig 3: Value of leakage confidence factor calculation.

Fig 3: Value of leakage confidence factor calculation.

Fig 4: Reverse image of three dimensional graph.
Acoustic noise logging involves identification of recorded noise generated from a leak, followed by a comparison of noise amplitude information at different locations to determine the location of the leak. It is a non-intrusive technique where the cost of deployment is minimal.

Working closely with some of the UK's leading water companies, Primayer Ltd launched its range of Phocus® intelligent noise loggers earlier this year to address the shortcomings of previous acoustic noise loggers. Offering up to 10 years' battery life, the new units were also nearly half the previous size and weight, allowing the noise logger to fit into the smallest chambers and onto valve spindles where the covers could then be closed.

The Phocus®2 has additional features such as a 'logical' display of leak noise strength and a leak confidence factor enabling field teams to take on-site action without the need for downloading to laptops. This significantly speeds up the leak detection process. Size has been reduced further and up to 15 units can be packed into portable cases.

Loggers are currently on trial in Australia, Germany, South Korea, Thailand, France, the USA and elsewhere. In the UK both Thames and Southern Water are using the Phocus®2 to help further reduce leakage, particularly in problem District Meter Areas (DMAs) where leakage was initially indicated by minimum flow readings.

Cost saving surveys
Precise identification of leaks within the DMA allows field teams to accurately pinpoint excavation sites for remedial work. Phocus®2 can store data from successive surveys of the same site, thus building a leakage history. The data stored is linked to specific valves, identified on detailed Ordnance Survey network plans, so repeated surveys can be carried out on the same site with minimum effort.

When Southern Water completed a study of a number of DMAs, calculations indicated that the cost of leak location using Phocus®2 works out to be one third of the conventional survey costs per property.

Because each DMA can be effectively surveyed within 2 days of notification with minimum extra time and labour, overtime has been reduced and economic levels of leak detection improved using existing manpower. This reduction is due to the ability to target specific areas of interest more effectively within the DMA.

By keeping computerised records, Southern Water's field teams' efficiency has improved and indications are that the cost of noise logger systems will be recovered within a twelve-month period.

Maps and graphics
Using Phocus®2 data in conjunction with street maps and valve, hydrant and fitting location a single operator can receive exact information of the contact points to be used for each Phocus unit. Current practice enables 60 units to be collected and interrogated each morning and redeployed in the afternoon.

Once the data has been downloaded, Phocus software allows easy access to tabular data of the results as well as 2 & 3D graphics. Tabulations can then be annotated and copies directed to the site personnel to indicate points to be correlated. Descriptions of the leaks can subsequently be added to enable comprehensive records to be kept. In locations where, for example, electricity sub-stations produce constant background noise, subsequent surveys would note this information and take appropriate action when setting out for succeeding surveys.

Vehicle costs are also reduced since the noise loggers have a battery life of 10 years, require no heavy charging equipment and can store data for up to three months. Phocus®2 is normally supplied in a portable rigid case, containing 15 loggers. Each case can be connected together to form a system comprising any number of noise loggers. Southern Water carries out surveys each night for a 2-hour period of minimum usage and highest pressures - but sets out the units the previous day, recovering them the following morning. This enables suspect areas to be identified and correlated during that day and in practice means that within two working days of the DMA data indicating an increase in consumption, the team can achieve:

  • Prelocation of the leak with Phocus®2 loggers
  • Pinpointing the leak with a Eureka calculator
  • Confirmation with ground microphone/listening stick
  • Repair of the leak

Because pipe repairs are carried out in-house, it is possible to claim consistent time scales of seven working days from initial indication of a leak to completion of repairs.

Southern Water has substantially reduced the cost of surveying for leakage as the data necessary for setting out the loggers in the identical locations for successive surveys is readily available. This is illustrated by an example of a cost-effective survey carried out in Southampton. The Savings have been achieved in terms of man hours as illustrated in the box below.

Better leak detection
From experience to date, Southern Water expects to identify 3-8 leaks each night from every set of results. This means some 20 leaks per week are located and eliminated. Southern Water uses contract and direct labour to install, locate, collect, download and re-programme the Phocus®2 noise loggers and the system has increased cost savings and efficient monitoring. One of the features that has proved important in the interpretation of the results is the leakage confidence factor calculation which identified the presence of leakage, even where the 'spread' of the recorded sound levels may be substantial. The conventional wisdom is that for large spreads there is no leak, but Southern Water has proved that with the patented leakage confidence factor algorithm, there are occasions where Phocus®2 has indicated otherwise - i.e. a leak was subsequently proved to exist.

Figure 3 is an example taken from 06A58 at Chickhall, which illustrates the value of this calculation in that the spread was 18 decibels with the critical value of the 27dB and the peak of 28dB. In this example, the spread value would probably have eliminated the conclusion of the possibility of a leak using accustomed methods of interpretation. However, the noise from the leak was supplemented by 'draw off' noise, which distorted the spread figure. The leakage confidence factor algorithm used in Phocus®2 will correctly recognise the leak despite the presence of the 'draw off' noise.

This effect is clearly illustrated in figure 4 where the reverse image on the 3D screen shows the consistently sharp rise from the critical to the peak value. The tabulation presented for each logging run of results categorises the possibility of leakage into four groups and from which appropriate actions can be initiated.

In sensitive areas it is felt that the number of unexpected bursts has been reduced due to the practice of regular surveys. Potentially disruptive failures are detected at an earlier state enabling more accurate data to be stored and analysed, and to predict where mains rehabilitation is becoming pertinent.

Phocus®2 loggers will be on demonstration at Aquatech.



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