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Water utilities and developers
Presentations and publications
Modern leak detection practices
As the demand for water continues to increase both in the UK and overseas, there is greater pressure on water utilities to operate their distribution systems more efficiently. One very important activity is the reduction and control of water loss from these systems.The starting point of a water loss reduction programme is to fully assesshow much,where and why water is lost and then develop a strategy to reduce losses to an economic or socially acceptable level with the appropriate mix of nonrevenue water reduction activities.
This article outlines some theory with regards Leakage, Leak Detection/Localising, leak Location, and also Emerging Innovative Technology. The article outlines the importance of an active leakage control programme. This can best be described as a proactive strategy to reduce water loss by the detection of visible and non-visible leaks by highly trained engineersand technicians using specialisedequipment followed by the prompt repair of leaks.The efficient location of visible and nonvisible leaks and bursts in a water distribution system and their prompt repair represent two of the four basic leakage management techniques as shown in the diagram.
In the diagram the rectangular box represents the total real losses (leakage) of a water utility and this can be reduced until just minor leaks are left escaping from a system and these are known as the unavoidable annual real losses (UARL).In most cases the economic level of losses will be greater than the UARL. Before examining the equipment and techniques used by leakage engineers and technicians one must consider the main factors that influence leakage:
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Infrastructure condition |
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Pressure |
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Number of service connections |
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Length of mains |
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Annual number of new leaks (reported and unreported). |
Average run-time of reported and unreported leaks The frequency at which new bursts and leaks occur depends upon the overall condition of the infrastructure and how well the pressure is managed. Dependent upon the specificground type there willalwaysbe a proportionof leaks that do not appear on the surface Le.nonvisible leaks and these need to be detected.
Leak detection or localising leak Detectionisthe 'narrowingdown'or localisingof leak/leaksto a section of pipe work in a distribution system.The most popular way of achievingthis is firstly, to create small discrete sectors within the distribution system. These are known as District Meter Areas (DMAs). A DMA is an area commonly containing between 1000 to 3000 service connections within which water measurements can be readily made and analysed to determine the level of leakage.
If the level of leakage rises in a DMA then a survey is carried out to determine in which part of the DMA the loss is occurring.One of the most efficient ways of achieving this is through the use of acoustic loggers.They are used to define the general area Le.the street or section of pipe in which leaksare occurring.They are installed on pipe fittings by way of a strong magnetand are programmed to listen for leak characteristics. By recording and analyzing the intensityand consistency of noise,each logger indicates the likely presence (or absence) of a leak. Acoustic loggers can either be permanently located in the network or they can be deployed at certain points for a user definable period often two nights.
Leak location
The next activity for the leakageengineer is to precisely locate or pinpointthe position of the leak and mark the point clearly on the ground surface where the repair teams will have to excavate. There are several methods that can be utilised to pinpoint the leak or burst and as new pieces of equipment are developed techniques change and evolve.It is also true that some pieces of leak location equipment work better on some distribution systems rather than others. None of the methods are totally infallible and the skill and motivation of the leakage engineer in the pinpointing of a leak cannot be underestimated.
One of the simplest leak location tools is the ground microphone. It can be used for locating leaks by fixing it onto a fitting, such as a sluice valve,or it can be used on the ground surface directly above the pipeline.In this indirect sounding survey technique, the ground microphone is moved along the surface with the operator noting the changes in sound amplification as the microphone nears the position of the leak.
The efficiency of leak location has changed dramaticaly since the introduction of the leak noise correlator in the late I970s. Similar to the traditional sonic equipment the correlator relied upon the noise generated bya leak on a buried pipeline. The fundamental difference however, was that the leak noise was picked up by sensors deployed at two locations e.g. two valves on the pipeline either side of the leak.The difference in the arrival time of the leak noise at each sensor; coupled with the knowledge of the pipe material,diameter and length,enablesthe leakto be pinpointed precisely.
During the following 25 or so years the correlator devel- opedfrom beingthe sizeof a large safethat took two men half a day to find a leak to a device that almost fitted into 11 the palm of your hand and leaks can be pinpointed in minutesrather than hours.In 2002 the digital correlato~ was developedoffering the followingadvantagesover its analoguepredecessor:
- Superior leak location performanceon all pipematerials (especially plastic) and sizes.
- Quicker and easier to use,especiallyfor lessexperiencedoperators .
- No interferenc.eor data loss in digital radio transmissions
In the first year of the 21st century a combined acoustic loggerand leaknoise correlator was developed. This systemhasthe advantage of reducing the wait time between identification of a leak noise and pinpointing of the leakthus reducingthe run time for the leak and possib~ the cost of repair.
Emerging technology
The pace of the development of new technology has quickened in the last 10 to 15 years as the goal of many water utilities around the world to reduce water loss has become a priority. In particular correlators have advanced rapidly in the last two or three years and now include simultaneous multicorrelation systems,cordless accelerometer radio link systems and PDA (PDA) based units. Some of these systems have a built in GPS (global positioning system) and this links to the GIS (geographic information system - a databaseof the network) incorporated within the machine. Internal noise/leak indicators have been developed in recent years and this is now seen as the approach that will locate the smallest of leaks.
These methods use the process of a noise recorder beingdeployedinto the water within the pipe using the velocity of the water to carry the equipment along. Some of this equipment is now smaller than a tennis ball but still has to be inserted into the water main by a safe and suitable method and also has to be retrieved in a similar manner. This equipment travels along the pipe listening and when a noise is heard this is transmitted to sensors strategicaly placed along the route of the main to receive the data. These units are also used to ascertain the water quality and chemical composition of the water.
The future
It is the dream of leakage engineers to havea pieceof equipment that will find every single leak on a section of pipe at the first attempt.Will this dream become reality in the next decade?
This article was written by Richard Pilcher; Principal Operations Engineer at Halcrow.
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