GB2062877A - Method and device for detecting leaks from pipelines - Google Patents

Abstract

To detect leaks from pipelines carrying fluids, especially oil, light is transmitted through a fibre-optic 3 held in proximity with the pipeline. The fibre-optic is surrounded by a medium 4 e.g. silicone rubber of which the refractive index is altered by the influence of the leaked fluid. Oil soaks into the medium through a permeable cladding (1) and elastomeric protective layer (2), and increases its refractive layer sufficiently to render the fibre optic non-internally-reflective so that light (5) is absorbed. Control means linked to a light receiver detect that change and the position of the leak is located to within the length of the fibre optic. In another embodiment the medium is a liquid which is expelled from around the fibre optic by the action of leaked fluid. <IMAGE>

Description

SPECIFICATION Device and method for detecting leaks from pipelines The present invention relates to the detection of leakages from pipelines.

It is becoming increasingly important not only from the economic point of view but also from the environmental point of view that leakages in oil, gas or other chemical pipelines shall be detected within a comparatively short time. Although catastrophic breaks will rapidly become evident, up to now the detection of small leaks and seepages has been very difficult especially when the pipelines are inaccessible, for example being under ground or under water.

The present invention sets out to detect such leakages by causing the medium leaking from the pipeline to change the environment around a light-conducting core such as a fibre optic which is adjacent to the pipeline.

The function of such cores is to conduct light as efficiently as possible and therefore they are surrounded by some medium which, having a lower refractive index than the material of the core, causes total internal reflection at the boundary of the core so that light is not lost from it.

The invention is based on the realisation that if that medium becomes changed into one which has an equal or preferably a higher refractive index than the core material then light incident on the wall of the core will be able to escape from it and, from the point of view of a detector positioned along the core, light will appear to have become extinguished or at least attenuated.

In one form of the present invention the core is surrounded by an elastomeric sheath which in principle is conventional and normally has a refractive index less than that of the core. This elastomer is usually a siliconebased rubber. This core is placed in juxtaposition with the pipeline, preferably running along parallel with it and attached to it. If oil or other liquid chemical escapes from the core it will seep into the silicone rubber which is permeable to such materials, will come into contact with the core and cause a change in its internal reflectivity and hence in its light conductive capacity. At suitable intervals along the pipeline light emitters and detectors are positioned so that loss of light conductivity within a given portion of the core is detected and signalled to a control station.

In another form of the invention which is useful especially when the pipeline is under water and also when the material within the pipeline is of a lower refractive index than the core, the core is surrounded by a liquid sheath which has a lower refractive index than the core. The sheath is entrapped within ducting which contains also a comparatively dense liquid such as water (or is open to external water surrounding the pipeline) and which has a closed head above the core. Material seeping from the pipeline is trapped in the closed head and therefore tends to displace the liquid sheath from around the core When it has so displaced the sheath, the reflectivity of the core changes.If the refractive index of the material from the pipeline is lower than that of the core so that displacement of the sheath would continue to give internal reflection then the ducting includes also a third liquid. This third liquid is of lower specific gravity than the liquid of the sheath but has a higher refractive index than the core so that as the liquid sheath and the third liquid are displaced by material which leaks from the pipeline and is trapped in the duct, the third liquid is brought into contact with the core and being of higher refractive index lessens its conductivity as before.

Particular embodiments of the invention will now be described with reference to the accompanying drawings wherein: Figures 1 and 2 show a first embodiment of detector having a solid permeable sheath, seen in radial section and in two conditions, Figure 3 show a second embodiment in cross-section with no leak occurring, Fi~ ure 4 shows the second embodiment with a leak occurring, Figure 5 shows a sectional view of a pipeline with t.e first embodiment juxtaposed with it, and Figure 6 shows diagrammatically a side view of a length of the pipeline of Fig. 5.

In the first embodiment, which is at present the preferred embodiment, a leak detector device takes the form of a cylindrical object of indefinite length of which the outer wall is a cladding 1 which is perforate or otherwise permeable and which has within it a protective layer 2 of foam rubber or like elastomer which is open-celled or otherwise permeable.

At the centre of the cylinder is housed a light conductive core 3 such as for example a quartz fibre optic core surrounded by its conventionally solid sheath 4 of permeable material such as silicone rubber. The refractive index of the sheath 4 is normally lower than that of the quartz so that light, indicated at 5, suffers total internal reflection every time it is incident upon the wall of the core and is transmitted efficiently along that core. Referring to Fig. 6 light is injected into the core by a light source 1 7 positioned at appropriate distances along it, the distances being appropriate to the intensity of the light used and the core being used and also to the precision with which it is desired to locate leakages which might occur.There is also inserted adjacent each light source 17, but directed towards a remote such light source 17, a detector 1 8 for the light transmitted by the core and the sources and detectors are con trolled remotely.

They may be actuated continuously or intermittently. The detector is placed in juxtaposition with a pipeline 8 carrying oil or other liquid material having a refractive index higher than that of the quartz. It is very easy to secure the detector to the pipeline by e.g.

straps 9 or lay it so as to touch the latter. Two or more such detectors may be associated with a single pipeline being at different positions around its periphery. Any liquid such as oil 7 leaking from the pipeline can enter through the apertures in the perforated cladding 1 and as is seen in Fig. 2 it permeates the foam protective layer 2 and enters the sheath 3, causing (incidentally) swelling of the sheath. But when the material comes into contact with the outer wall of the quartz core, it will alter the reflective action of that core and when light indicated by arrows 6 is internally incident upon those walls, instead of total internal reflection there will be partial or complete loss of the light to the outside of the core. Such loss is recorded at the detector as an attenuation or extinction of the light source and the existence and the location of the leak is established.

The response time of this embodiment is a function of the permeability of the sheath to the leaking liquid (largely governed by its degree of cross-linkingj and can be adjusted by appropriate selection or modification of the sheath material, bearing in mind the material intended to be detected.

When crude oil is the conveyed fluid it is desirable to use particular silicone rubber materials in the sheath or to use particular quartz material as the conductive fibre.

Crude oil does not swell silicone rubber as much as some other liquids do and it also appears that some fractionation of the crude oil occurs during its absorption into the rubber.

Conventional quartz has a refractive index about 1.46 and silicone rubber about 1.41.

Probably for the reasons mentioned above crude oil absorbed by a silicone rubber sheath may not have the effect of extinguishing the internal reflections in the fibre.

For extinction to be assured when crude oil in the swelling medium, therefore, the difference between the refractive indices of the rubber and quartz must start off in the normal condition narrower than is indicated above, and a silcone rubber of a refractive index of between 1.42 and 1.44 inclusive should be used. Such rubbers are commercially available and an example is Grade OF-8 from Shinetsu Chemical Company, 6-1 2-chome, Ohtemachi, Kyoda-ku, Tokyo, Japan. Alternatively (or additionally) the refractive index of the quartz used may be somewhat lower than is conventional.

In the second embodiment shown in Figs. 3 and 4 there is shown an arrangement particularly suitable for use when the pipeline is under water and/or for use when the material conducted by the pipeline has a refractive index lower than that of the quartz.

In this arrangement, the pipeline 8 has around at least its upper part a cover 11 which includes a duct 1 2 within which runs a quartz core 3. The duct 1 2 is downwardly open but has a closed head at its upper end.

The cover is filled with water except at the upper part of the duct 1 2 where the core 3 is normally surrounded by a sheath of silicone oil 1 3. This is an oil with a refractive index lower than that of the material of the core 3 so that the core remains internally reflecting.

If the oil or other liquid contained by the pipeline has a refractive index higher than that of the quartz core, then leakage of the liquid will be detected by the leaking liquid being caught by the cover 11 and rising into the duct 1 2 so that it displaces the silicone oil downwards until the core 3 is surrounded by the leaked liquid. At this stage, light within the core ceases to be totally internally reflected and the change can be detected as the first embodiment.

If however the material in the pipeline is a gas or is a liquid which has a lower refractive index than the core, then a further liquid 14 immiscible with the silicone oil is entrapped above the latter within the duct, this third liquid 14 having a specific gravity intermediate between that of the silicone oil and the escaping material. It includes a dyestuff or other light absorber. When material escapes from a leak 10 in the pipeline 8' and is trapped within the duct, as indicated in Fig.

4, the third liquid 14 is displaced downward until it surrounds the core 3, the trapped material occupying the volume 1 5 and the silicone oil being seen below the core at 1 3.

Once more the effect is to change the refractive index of the material surrounding the core 3 and hence its light-conductive capacity.

Obviously it is possible within the framework of this second embodiment to cause a change in conductive condition of the core by displacing from around the core a liquid layer of higher refractive index by means of an escaping material with lower refractive index so that leakage is indicated by the beginning of light transmission along the core rather than by its cessation or attenuation.

Claims (12)

1. A device for detecting leakage of fluid from a pipeline adjacent the device which device includes a fibre-optic core of a first refractive index and normally surrounded by a medium of a second refractive index and means for allowing access of leaked fluid into the device to cause a change in the refractive index of the or a medium surrounding the core to tend to at least annul the difference between the first and second refractive in dices.

2. A device according to claim 1 wherein the medium is a solid, the effect of the leaked fluid being to change the refractive index of the solid.

3. A device according to claim 2 wherein the means for allowing access include a permeable elastomeric layer surrounding the solid medium and a permeable casing around the elastomeric layer.

4. A device according to claim 1 wherein the medium is a liquid which is expelled from around the core by the action of the leaked fluid and is replaced by another fluid.

5. A device according to any one of the preceding claims wherein the first refractive index is higher than the second refractive index.

6. Devices substantially as herein described with reference to and as illustrated in the accompanying drawings.

7. A method of detecting leakage of fluid from a pipeline, wherein the leaked fluid is brought into the vicinity of a fibre-optic core of a first refractive index so as to change the refractive index of a medium surrounding the core and thereby change the light-conducting characteristics of the core, and detecting the said change to establish the occurrence of a leakage.

8. A method according to claim 7 wherein the change detected is an attenuation or extinction of light received via the fibre-optic core at a receiver from a light source.

9. A method according to claim 8 wherein the change is caused by permeation of a solid medium surrounding the core by a liquid leaked from the pipeline.

10. A method according to claim 9 wherein the liquid is oil.

11. A method according to claim 7 or claim 8 wherein the change is caused by the leaked fluid expelling a liquid medium from around the core and replacing it by a different material.

12. Methods substantially as herein described with reference to the accompanying drawings.