GB2246633A

GB2246633A - Improvements in or relating to leak location

Info

Publication number: GB2246633A
Application number: GB9015275A
Authority: GB
Inventors: Martin Keith Partridge
Original assignee: BROWNELL Ltd
Current assignee: BROWNELL Ltd
Priority date: 1990-07-11
Filing date: 1990-07-11
Publication date: 1992-02-05
Also published as: GB9015275D0

Abstract

In order to detect the position of a leak in a pressurised pipe or the like, a sensor which is responsive to a change in relative humidity is moved in the vicinity of the pipe until a change in relative humidity is detected. The change in relative humidity is caused particularly when the gas in the pipe is a dry gas. The sensor may comprise a dielectric element which has properties dependent on the quantity of moisture absorbed by the dielectric material.

Description

DESCRIPTION OF INVENTION "Improvements in or relating to Leak Location THE PRESENT INVENTION relates to leak location and more particularly relates to the location of leaks in hermetically sealed vessels or in elements such as pipes or conduits.

Leaks can be a problem in many different situations. For example, if there is a leak in a pipe or conduit carrying high-pressure gas, then that gas will be lost. This may be inconvenient, if the gas is com- pressed air, for example, but may be very dangerous if the gas is natural gas or some other flammable or polluting gas. Similarly, when a housing has been made which is intended to be hermetically sealed, such as a housing, in which delicate equipment is to be located, intended to maintain a clean, de-humidified atmosphere, then leaks in the housing may be very inconvenient.

At the present point in time it is possible to determine whether there is a leak present in a housing or conduit, by pressurising the housing or conduit and monitoring the pressure. A fall in pressure indicates the presence of a leak. Such techniques may be very sensitive, enabling very small leaks to be detected, but these techniques do not provide any information as to the precise location of the leak.

It has been proposed previously to utilise various types of detector to detect the location of a leak. One type of detector works on an ultrasonic principle and effectively utilises an ultrasonic transducer which responds to the ultrasonic energy generated by a stream of gas passing through the leak. In other words, the transducer responds to a "whistle" or other noise given off by the gas. Such an arrangement may be utilised where the gas escaping through the leak is under a very high pressure, for example, several bars or more, but such a technique is not of any real value where the pressure of the gas is very low. A further technique that has been proposed before relies on a sensor that is responsive to thermal conductivity of gas.The sensor initially provides a signal representative of the thermal conductivity of the ambient atmosphere, but if this atmosphere becomes contaminated with gas escaping from the conduit or housing being investigated, then the thermal conductivity, as measured, will differ from an ambient. Such an arrangement does, however, absolutely rely on the fact that the gas escaping through the leak has different thermal properties to those of the ambient atmosphere. Thus, this technique cannot readily be use with compressed air, or nitrogen for example.

A further technique that can be utilised, especially in connections with housings which can only be subjected to a very slight pressure, is to immerse the housing, when pressurised, in a tank of water and then to observe where bubbles emerge from the housing. This technique is inconvenient, in that the housing has to be manoeuvred into the tank of water, and also the housing may be made of a material that is not really adapted to withstand immersion in water. For example, if the housing contains iron or steel components, care must be taken to ensure that a rusting process is not initiated by the immersion in water. Also this technique cannot readily be utilised with pipes or the like which are permanently mounted in position.

The present invention therefore seeks to provide a method of, and an apparatus for, determining the location of a leak.

According to one aspect of this invention there is provided a method of detecting the position of a leak in a vessel, pipe, conduit or the like containing gas at a pressure higher than the pressure of the ambient atmosphere, said method comprising the steps of taking a sensor which is responsive to a change in relative humidity, monitoring signals from the sensor and moving the sensor in the vicinity of the pipe until a change in relative humidity is detected.

Preferably the gas is a substantially dry gas.

Conveniently the method comprises the steps of intially supplying substantially dry gas to the vessel, pipe or conduit.

Advantageously the sensor comprises an element of dielectric material, the electric materia; having dielectric properties dependent upon the quantity of moisture absorbed by the dielectric material.

Preferably the dielectric material comprises a metal oxide, such as aluminium oxide.

Conveniently the dielectric material is associated with two electrodes, electrodes being connected to an impedance monitoring circuit adapted to monitor the impedance of the dielectric material.

Preferably the sensor comprises a conductive ceramic substrate forming one electrode laminated with the said dielectric material which constitutes the other electrode.

Advantageously the sensor is associated with an alarm which provides a visual or audible alarm when a change in relative humidity is detected.

According to another aspect of this invention there is provided a leak detector apparatus to detect leaks in a vessel, pipe or conduit containing gas at a pressure greater than the pressure of the surrounding ambient atmosphere, the leak detector comprising a sensor adapted to sense a change in relative humidity and circuitry adapted to receive signals from the sensor and adapted to activate an alarm when a change in relative humidity is detected.

Preferably the sensor comprises an element of dielectric material, the dielectric properties of the dielectric material are dependent upon the moisture absorbed by the dielectric material.

Conveniently the dielectric material comprises a metallic oxide, such as aluminium oxide.

Preferably the dielectric material is associated with two electrodes, connected to an impedance monitoring circuit which comprises said circuitry.

Conveniently the dielectric material is mounted on a conducting ceramic substrate.

Preferably the ceramic substrate and the dielectric material comprise the said electrodes.

Advantageously the sensor incorporates an alarm, such as a visual alarm, or an audible alarm.

In order that the invention may be more readily understood, and so that further features thereof may be appreciated, the invention will now be described, by way of example, with reference to the accompanying drawing which is a perspective view of a sensor element for use in accordance with the invention and a block diagram of the associated circuitry.

A leak detector in accordance with the invention comprises a sensor 1, formed of a substrate of conductive ceramic material 2 having formed thereon an electrode 3 of metal oxide, such as aluminium oxide The metal oxide is of a porous nature. The substrate and the electrode of the sensor are connected by appropriate leads to the input terminal of an impedance monitoring circuit 6. The impedance monitoring circuit forms part of a sensor circuit 7, which, in turn, is connected to an appropriate alarm device 8. The alarm device may be an audible alarm or a visual alarm, such as a flashing light or a moving needle meter.

The porous metal oxide 3 of the sensor is, in use, adapted to be exposed, and it is to be understood that the dielectric properties of the alumin um oxide depend upon the amount of moisture present in the aluminium oxide. The aluminium oxide is slightly hygroscopic, and thus absorbs moisture from the atmosphere to which the aluminium oxide is exposed. Thus, if exposed to a damp atmosphere of high relative humidity, the aluminium oxide will contain a relatively high amount of water, whereas if exposed to a dry atmosphere the aluminium oxide will contain a relatively low amount of water. The impedance as measured by the impedance monitoring circuit will, as is known to those skilled in the art, depend upon the degree of moisture present within the aluminium oxide.

The present inventor has found that when a sensor of the type described above is located in a stream or moving gas, particularly a stream of moving gas which is substantially dry, the quantity of moisture contained within the aluminium oxide becomes reduced, as compared with the quantity of moisture present when the sensor is just exposed to the ambient atmosphere. The sensor circuit is adapted to respond to this change in impedance and to activate the alarm.

The sensor 1 will be mounted on an appropriate probe, so that the metal oxide electrode 3 is exposed.

It is thus to be understood that the apparatus, as described above, may be utilised to locate a leak 9 in, for example, a high-pressure pipe-line 10, by moving the sensor until the sensor is in such a position that the air or gas 11 escaping from the pipe-line impinges on the sensor, at which time the impedance measured by the impedance detecting circuit will change. An audible or visible alarm 8 will then be activated, so that the person moving the sensor will know that the position of the leak has been detected.

Similarly it is to be appreciated that when a housing, such a housing adapted to contain sensitive equipment, which is intended to be hermetically sealed against the atmosphere, is being tested, the housing will initially be pressurised, to a pressure slightly in excess of atmospheric pressure, with a gas which is substantially dry. If there are any leaks present in the housing the gas within the housing will escape through the leaks. The escape rate may be very low, in view of the low-pressure differential between the interior of the housing and the ambient atmosphere, but since the gas is dry, and the atmosphere is, at least usually, moist to a certain extent, when the sensor is located in the path of the gas leaking from the housing, the quantity of moisture present on the aluminium oxide will be reduced, thus again activating the sensor circuit 7 and the alarm 8.

It may well be, that the sensor circuit utilises another sensor element 1, identical with the first sensor element 1, as a "standard". Both these sensor elements will ordinarily be exposed to the ambient atmosphere, but only one sensor will be moved to be in the stream of gas emerging from the pipe or vessel being investigated.

It is envisaged that the method as described above may be utilised in connection with any housing which is to be hermetically sealed, and even may be utilised in connection with housings which are, in use, intended to be evacuated or subjected to a partial vacuum. Equally the method may be utilised to detect gas leaks from high-pressure pipe-lines, or other pipe-lines containing gas at an over-pressure, such as domestic gas supply pipes. The entire apparatus may be designed to be portable, so the apparatus can be utilised in connection with fixed pipe-work without any undue inconvenience.

It is enivsaged that the apparatus as described may be utilised to detect a leak having a flow rate as low as 0.001 cc per second.

Whilst the invention has been described with reference to one specific embodiment it is to be appreciated that modifications may be effective without departing from the scope of the invention as defined by the following Claims. Any appropriate form of sensor that is adapted to measure ambient moisture or humidity levels may be utilised, provided that it has an appropriate degree of sensitivity. It is preferred to utilise a sensor including a sensor element formed of a material having dielectric properties which are responsive to ambient moisture levels or ambient relative humidity, so that the change in the dielectric properties may be measured as a capacitive change or as a change of impedance. The dielectric material may be utilised in conjunction with two separate electrodes, although it is preferred that the dielectric material actually forms one of the electrodes.

Claims

CLAIMS:

1. A method of detecting the position of a leak in a vessel, pipe, conduit or the like containing gas at a pressure higher than the pressure of the ambient atmosphere, said method comprising the steps of taking a sensor which is responsive to a change in relative humidity, monitoring signals from the sensor and moving the sensor in the vicinity of the pipe until a change in relative humidity is detected.

2. A method according to Claim 1 wherein the gas is a substantially dry gas.

3. A method according to Claim 1 or 2 wherein the method comprises the steps of intially supplying substantially dry gas to the vessel, pipe or conduit.

A A method according to any one of the preceding Claims wherein the sensor comprises an element of dielectric material, the dielectric material having dielectric properties dependent upon the quantity of moisture absorbed by the dielectric material.

5. A method according to Claim 4 wherein the dielectric material comprises a metal oxide.

6. An arrangement according to Claim 5 wherein the metal oxide comprises aluminium oxide.

7. A method according to any pne of Claims 4 to 6 wherein the dielectric material is associated with two electrodes, electrodes being connected to an impedance monitoring circuit adapted to monitor the impedance of the dielectric material.

8. A method according to Claim 7 wherein the sensor comprises a conductive ceramic substrate forming one electrode laminated with the said dielectric material which constitutes the other electrode.

9. A method according to any one of the preceding Claims wherein the sensor is associated with an alarm which provides a visual or audible alarm when a change in relative humidity is detected.

10. A leak detector apparatus to detect leaks in a vessel, pipe or conduit containing gas at a pressure greater than the pressure of the surrounding ambient atmosphere, the leak detector comprising a sensor adapted to sense a change in relative humidity and circuitry adapted to receive signals from the sensor and adapted to activate an alarm when a change in relative humidity is detected.

11. An apparatus according to Claim 10 wherein the sensor comprises an element of dielectric material, the dielectric properties of the dielectric material are dependent upon the moisture absorbed by the dielectric material.

12. An apparatus according to Claim 11 wherein the dielectric material comprises a metallic oxide.

13. An apparatus according to Claim 13 wherein the metallic oxide comprises aluminium oxide.

14. An apparatus according to Claim 11, 12 or 13 wherein the dielectric material is associated with two electrodes, connected to an impedance monitoring circuit which comprises said circuitry.

15. An apparatus according to Claims 11 to 14 wherein the dielectric material is mounted on a conducting ceramic substrate.

16. An apparatus according to Claim 15 wherein the ceramic substrate and the dielectric material comprise the said electrodes.

17. An apparatus according to any one of Claims 11 to 16 wherein the sensor incorporates an alarm.

18. An apparatus according to Claim 17 wherein the alarm is a visual alarm.

19. An apparatus according to Claim 17 wherein the alarm is an audible alarm.

20. A method of detecting a leak substantially as herein described with reference to the accompanying drawing.

21. A leak detector apparatus substantially as herein described with reference to and as shown in the accompanying drawing.

22. Any novel feature or combination of features disclosed herein.