GB2338072A

GB2338072A - Leak detection

Info

Publication number: GB2338072A
Application number: GB9811934A
Authority: GB
Inventors: Mark Ian Wareing
Original assignee: AEA Technology PLC
Current assignee: Ricardo AEA Ltd
Priority date: 1998-06-04
Filing date: 1998-06-04
Publication date: 1999-12-08
Also published as: GB9811934D0

Abstract

For detecting the location of leaks from a pipeline 11 which is used for transporting liquid, a tracer gas eg. helium is introduced into the liquid in solution. The gas remains in solution under the inherent pressurisation of the liquid as it flows through the pipeline, but gas is released at a leak 46, where depressurisation occurs. A detector 42,44 for the gas is moved along or close to the path of the pipeline 11.

Description

1 - Leak Detection The invention relates to a method for detecting the

location of leaks from a pipeline which is used for transporting liquid and more particularly from mains water pipelines.

It is known to detect leaks in vessels and associated pipework by injection of a tracer gas, usually helium, and using a mass spectrometer with a portable 'Isnifferll probe to search the apparatus under test 1 for signs of emerging tracer gas. This approach is only appropriate for a relatively contained assembly of vessels and pipework and has to be carried out while the apparatus is out of service and, generally, cleared of the operating fluid which it contains in use. The present invention provides a solution to the problem of detecting and, more importantly, locating leaks in very large networks of pipeline, such as those used for the supply of mains water, and this can be done without interrupting or interfering with the normal operation of the pipelines. In some circumstances, it may still be more convenient to interrupt supply, for example isolating a part of the network for testing, but this can be carried out with minimum impact upon the quality of the supply.

Accordingly, the invention provides a method for detecting the location of leaks from a pipeline which is used for transporting liquid, which method comprises introducing into the liquid which is to flow through the pipeline a gas, the presence of which gas is detectable in air, in such a manner that the gas is carried in solution --'In the liquid, whereby depressurization of the liquid, which occurs where liquid escapes at a leak, causes release of gas from solution, and moving a 2 - detector for the gas along or in the neighbourhood of the path of the pipeline through which said liquid with gas in solution is flowing.

An inert and/or non-toxic tracer gas is required to be used when the method is applied to the testing of mr:

ains water pipelines, but is, of course, advisable for most or all applications of the method.

Conveniently the gas comprises a mixture of two or more separately detectable constituents.

Preferably the gas, or a constituent of the gas, comprises helium and a most convenient form of detector 15, for the gas is a portable spectrometer. A position sensor may be used to provide an indication of the position of the detector and thus of a leak when detected by the detector. Preferably the position sensor comprises a satellite global position receiver (GPS) and it is convenient to provide for signals from the detector and the position sensor to be automatically combined and recorded to provide a data record of detected leaks and their position.

A specific example of method and apparatus for carrying out the method embodying the invention will now be described with reference to the drawings filed herewith, in which:

Figure 1 is a highly schematic representation of a mains water pipeline buried below ground and a trolley for transporting detection equipmentover the path of the pipeline, Figure 2 is a diagrammatic representation of apparatus used for introducing helium in solution into the pipeline, Figure 3 is a block diagrammatic representation of components of detector equipment, and Figures 4 and 5 illustrate two alternative arrangements for introducing helium in solution into the 10. water in the pipeline.

Figure 1 shows a pipeline water and this will usually be level 12. A suitable location 15, region to be tested for leaks, solution into the water which normal usage of the pipeline, 11 for carrying mains several feet below ground is chosen, upstream of the for injection of helium in is flowing, as part of the therethrough.

The essential constituents of equipment for helium injection are illustrated in Figure 2 comprising a helium gas canister 13 with associated valve gear 14 connected via nonreturn valve 15, shut-off valve 16 and pressure gauge 17 to a helium injector device 18 (see Figures 4 and 5).

It may be possible to inject helium gas through a suitable form of diffuser directly into the water flowing in the pipeline 11 to create a "slug" of water containing helium in solution passing along the pipeline. However, it is preferred to ensure that a body of water is first prepared containing helium to saturation in solution and then inject this body of water into the pipeline.

Figure 4 illustrates an arrangement in which a loop 19 is connected to the pipeline 11 so as to bridge a main valve 21. The loop 19 contains a treatment chamber 22 - 4 into which there projects a gas pipeline 23 terminating in a diffuser 24. Valves 25 and 26 are provided for controlling flow of water into and out of the loop 19.

After filling the loop 19 with water, the valves 25 and 26 are closed. Helium gas is bubbled through pipeline 23 and the diffuser 24 into the water in the treatment chamber 22 until the water is saturated with helium in solution. The valves 25 and 26 are then opened li-0. and the pressure differential which will normally exist across the main valve 21 will force the water out of the loop and into the main stream through the pipeline 11. If necessary, the pressure differential for driving flow through loop 19 can be increased by partially closing the main valve 21.

Figure 5 illustrates an alternative arrangement for introducing a "slug" of water saturated with helium in solution into pipeline 11. A chamber 27 is connected via valve 28 and pipe 29 to the mains pipeline 11. Gas pipeline 31 and diffuser 32 provide for introducing helium gas into the chamber 27. From the top of the chamber 27 there extends a combined vent /pressuri zat ion pipe 33 connected via switch valve 34 and shut-off valve 35 to vent 36, or via switch valve 34 and shut-off valve 37 to pressure gas canister 38. A pressure gauge 39 enables the pressure in the chamber 27 to be monitored.

With pipe 33 opened to vent at 36, the chamber 27 is initially filled with water by opening valve 28. Valve 28 is closed when chamber 27 is full and helium gas then bubbled into the water in chamber 27 until a saturated solution at a pressure corresponding to that of the water in the main pipeline is achieved. With pipe 33 now connected to pressure gas canister 38, valve 28 is opened and the gas pressure supply via pipe 33 controlled to drive the slug of water from chamber 27 into the main pipeline 11.

The slug of water containing a saturated solution of 5 helium is then carried with the flow along the pipeline 11 and, whilst the water pressure within the pipeline is maintained, can continue to carry the helium in solution over large distances. At a leak, however, the water pressurization is lost and helium gas is released from solution. Helium gas rises, passing through gas permeable materials and readily rising through thelground above the pipeline to the ground surface from which it will continue to move rapidly upwards through the air.

Referring to Figure 1 and Figure 3, equipment to be moved along the path of the pipeline 11 downstream from the point of injection of helium in solution is conveniently carried upon a trolley 41. In this example, the equipment comprises a helium mass spectrometer and pumping system 42, power for which is provided from power pack 43. A sniffer probe 44 is connected to the mass spectrometer 42. Also carried on the trolley 41 is a global position sensor and data logger 45 connected to an electronic data output from the mass spectrometer 42.

The trolley 41, with the helium leak detector system switched on and working correctly in the sniffer mode, is moved along the path of the pipeline 11, sampling the air at ground level in the region above the pipe. The expected reading on the detector should be at background level (which can be zeroed out) unless there is a source of helium in the vicinity. In this example, helium concentration and position are automatically recorded and simultaneously observed by the operator. The operator should note a rise in the concentration of detected helium to a maximum as the site 46 of a leak is

6 approached, and tail off as the site is passed. The operator then returns to the site of the maximum reading and moves at right angles to the previous direction of travel to establish more precisely the site of the leak, the position of which is then registered taking into account wind direction and speed. It will also be necessary to take into account the effect of any large areas of impervious material which may have shifted the point at which leaked helium arrives at the ground surface.

In the procedure described above there is no interruption or interference with the mains supply.

1 In some circumstances, however, it is convenient to isolate a region that is to be subjected to test. For example, to test a particular street, it may be desirable to close off the mains supply to that street first. After checking that users have closed their taps, or by temporaily closing the cocks on the spurs supplying each separate user property, water saturated with the tracer gas is injected into the street system and pressure, equivalent to mains pressure, applied and maintained for a sufficient time for the injected water to reach a leak site and be detected.

The invention is not restricted to the details of the foregoing examples. For instance, although helium is probably the most suitable tracer gas, other gases (neon, for example) may be used provided they will rise to the ground surface from the site of the leak and be detectable there in air. To improve confidence that the detection is of gas arising from a leak, and not from some other source, it may be desirable to employ two or more gases in a cocktail which provides a clear signature n the detector. Neon or SF6, for example, are gases 7 which could be used, either alone instead of helium, or in combination with helium. A disadvantage of SF6 is that it is heavier than air. Although likely to be, or become, detectable at the surface near a leak, it would tend to collect and remain in any trench or underground passageway where it could represent a hazard through risk of asphyxiation.

cl It will be appreciated that other forms of detector for gas may be used and other means for transporting the detector over the path of the pipeline may be used,! for example a motor vehicle or, for difficult terrain, a backpack, or even detection from equipment in an aircraft or helicopter may be possible.

is, The detection equipment may include a radio transmitter for communicating position and leak detection information directly to a central control.

8 -

Claims

1. A method for detecting the location of leaks from a pipeline which is used for transporting liquid, which method comprises introducing into the liquid which is to flow through the pipeline a gas, the presence of which gas is detectable in air, in such a manner that the gas is carried in solution in the liquid, whereby depressurization of the liquid, which occurs where liquid escapes at a leak, causes release of gas from solution, and moving a detector for the gas along or in the ' neighbourhood of the path of the pipeline through which said liquid with gas in solution is flowing.

15,

2. A method as claimed in claim 1, wherein the gas is an inert and/or nontoxic gas.

3. A method as claimed in claim 1 or claim 2, wherein the gas comprises a mixture of two or more separately detectable constituents.

4. A method as claimed in any one of the preceding claims, wherein the gas, or a constituent of the gas, comprises helium.

5. A method as claimed in any one of the preceding claims, wherein the pipeline is a mains water pipeline.

6. A method as claimed in any one of the preceding claims, wherein the detector is a portable spectrometer.

7. A method as claimed in any one of the preceding claims, wherein a position sensor is used to provide an indication of the position of the detector and thus of a leak when detected by the detector.

9

8. A method as claimed in claim 7, wherein the position sensor comprises a satellite global position receiver (GPS).

9. A method as claimed in the claim 7 or claim 8, wherein signals from the detector and the position sensor are automatically combined and recorded to provide a data record of detected leaks and their position.

10. A method substantially as hereinbefore described with reference to the drawings filed herewith.

15, 15313 LgWs