GB2457304A

GB2457304A - Detecting pipeline leaks by detecting interference between acoustic carrier waves transmitted along the pipeline and leak generated sound waves

Info

Publication number: GB2457304A
Application number: GB0802488A
Authority: GB
Inventors: Christopher Teal
Original assignee: Individual
Current assignee: Individual
Priority date: 2008-02-11
Filing date: 2008-02-11
Publication date: 2009-08-12
Anticipated expiration: 2028-02-11
Also published as: GB2457304B; GB2457304B8; GB0802488D0

Abstract

A wave guide is provided in close proximity to and extending along a surface in which a leak path could be formed. The surface may be the wall of a pipe, especially a subsea pipeline, and the waveguide may be clamped to the outside of the pipeline, mounted inside the pipeline, or may be the pipeline itself. A first sound wave signal is propagated as fluid passes through the leak path. A second sound wave signal is transmitted along the wave guide from one end to the other, and acts as an acoustic carrier wave. The second sound wave signal differs in frequency from the anticipated first sound wave signal. A third sound wave signal resulting from interference between the first and second signals is detected at the other end of the waveguide using an acoustic receiver. The spectrum of the third signal is analysed to determine whether there is a leak. The system may be bi-directional, in which case the location of the leak can be determined. The carrier wave can be made powerful enough to be transmitted over long distances through the waveguide, which means that leaks can be detected remotely over long distances.

Description

1 2457304

METHOD FOR DETECTING PIPELINE AND OTHER LEAKS

Worldwide the oil and gas industry rely on pipelines to transport crude oil and natural gas. Both environmentally and commercially, leaks from these pipelines are undesirable and it is becoming essential that pipeline owners and operators monitor for such events so that corrective action can be taken.

The present applicant has a long and successful history of developing and providing methods to detect leaks from both oil and gas pipelines for major oil companies. These are normally used when a leak is suspected or periodic maintenance demands it. The leak detection systems are normally mobile and are used to scan along the pipeline producing a data processed display of any leaks found.

The main methods of leak detection used today employ fluorescent dyes or acoustics.

The dye detection process requires the use of a means for detecting the existence of dye that has passed through a leak. The acoustics process is well known and uses hydrophones (microphones) to listen' to sounds created when fluid under pressure escapes through an orifice into another fluid. This method does work but has drawbacks such as range, directionality and ambient noise. A further acoustic method has been developed by the present applicant and uses active acoustics that fire a sonic signal at the pipeline and looks for changes in return signal that would indicate a fluid leak. This system is mainly for detailed work looking for leaks around joints, seals, etc. * ** * * * * ** *S**

* Disclosure of Invention

* .According to a first aspect of the present invention there is provided a method of leak * detection comprising the steps of providing: * :* a wave guide in close proximity to, and extending along, a surface in which * : * * urface a leak path could be formed by means of which fluid on one side of the surface could pass through along the path to the other side of the surface with the propagation of first sound wave signal characterising the leak; transmitting along the wave guide a second sound wave signal differing in frequency from the anticipated first sound wave signal; and detecting by means of the wave guide for an acoustic interference third signal caused by interaction between the first arid second signals.

According to a second aspect of the present invention there is provided a pipeline for the transmission of a first fluid along the pipeline; the pipeline being surrounded at least in part by a second fluid; and a wave guide extending along, or incorporated in, the pipeline with means providing that in the event of a leak from the pipeline resulting in the generation of a first acoustic signal the transmission of a second acoustic signal along the pipeline by way of the wave guide would result in the generation of a characteristic interference signal detectable at a predetermined location remote from the leak.

Typically the surface is a pipeline wall through which a first fluid is displaced and the pipeline acts to separate the first fluid from a second fluid outside the pipeline. In a first preferred version of the invention the wave guide is a member extending along the outside of the pipeline with means for injecting an acoustic signal at a first end of the member and an acoustic signal receiver at a second end of the member. In an alternative version the pipeline is adapted to act as the wave guide. * ** * * S * S. * *SS

* . The present invention arises from enquiries requesting permanent leak alarm systems 25. ,or installation on long subsea and terrestrial pipelines. The normal leak detection * methods available today cannot readily achieve this, unless a very large number of are mounted along the length of the pipeline, so a new approach is required.

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Any such system would need to have very long spacing between sensors in the region of kilometres.

The present invention is a method of reliably detecting leaks in pipelines, whether very long or very short, and will enhance safety, help protect the environment and save costs in terms of loss and down time in the event of pipeline failure.

The present invention makes use of wave interference to transmit leak generated sound signals over very long distances. Leak generated signals vary in amplitude depending on pressure difference across the leak, however, the signal spectrum generally shows that these sounds fall into defined frequency bands. The problem is that these leak generated sounds do not have the amplitude or frequency to carry far enough through the surrounding sea for detection of leaks remotely over long distances.

This invention relies on generating a powerful enough acoustic carrier wave of known spectra that can be transmitted over long distances through a wave guide placed parallel to the pipeline or can be the pipe itself such that a leak generated sound signal anywhere along the pipeline will, at that location, cause interference by adding it's frequency and amplitude components to that of the carrier wave. Frequency, amplitude, wave guide dimensions, internal wave guide medium and construction material are all related to the distance the carrier wave can travel. In the event of a leak, the acoustic signal will interfere with the carrier wave and cause the received signal at receiver end of the wave guide, or pipeline, to exhibit a modified spectrum that can S...

be analysed and compared to the no leak spectrum' It is the phenomenon of wave nterference and resultant spectral modification and beat' frequencies that will be used to determine the event of a leak. By making the system bi-directional, the relative strengths and frequency distributions can be analysed to make an assessment of the location of the leak.

The invention of the method of using wave interference for leak detection imposes no limit on the frequencies (acoustic to very high frequencies, i.e., Light, EM etc.), wave amplitudes, and wave guide construction and dimensions that can be used nor whether the guide is clamped to the outside of the pipeline, mounted inside the pipeline, within the pipeline walls, the pipeline wall, or the guide is the pipeline itself. In addition, although the invention relates mainly to subsea pipeline leak detection, it equally applies to leak detection in terrestrial pipeline systems, industrial systems, power plants etc. The invention allows for leak detection of any fluid, whether liquid or gas, leaking into any surrounding medium whether liquid or gas.

Brief description of Drawings

Figures 1 (a) to (c) show diagrammatically an interference effect arising between two waves of different frequencies; Figure 2 is a diagram showing an external wave guide applied to a pipeline; and Figure 3 is a diagram showing an internal wave guide applied to a pipeline Figure 1 These show an interference effect arising form two waves of different frequencies -not to any particular scale and for illustrative purposes only. * .* * * I * I.

* .. . Figure 1(a) represents a first signal generated by a leaking fluid from a pipe leak. It has been found that such signals have a frequency and amplitude which are characteristic *.of a leak. ** I. * I I * I

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Figure 1(b) represents a second signal generated by means of a separate acoustic generator and transmitted along the wave guide of the present invention. The second signal characteristics are selected to provide for generating a significant interference pattern when imposed on a first signal generated of a likely leak. The resulting interference signal is readily transferred by means of the wave guide to a location where data processing is used to determine the location of the leak or leaks. * ** * I * * I. I... * I

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Claims

Claims 1 A method of leak detection comprising the steps of: providing a wave guide in close proximity to, and extending along, a surface in which surface a leak path could be formed by means of which fluid on one side of the surface could pass through along the path to the other side of the surface with the propagation of first sound wave signal characterising the leak; transmitting along the wave guide a second sound wave signal differing in frequency from the anticipated first sound wave signal; and detecting by means of the wave guide for an acoustic interference third signal caused by interaction between the first and second signals.
2 A method of leak detection as claimed in Claim 1 wherein the wave guide is a member extending along the outside of the pipeline with means for injecting an acoustic signal at a first end of the member and an acoustic signal receiver at a second end of the member.
3 A method of leak detection as claimed in any preceding claim wherein the pipeline is adapted to act as the wave guide. * I. S... * S *S55
4 A pipeline for the transmission of a first fluid along the pipeline; the pipeline *...being surrounded at least in part by a second fluid; and a wave guide extending along, or incorporated in, the pipeline with means providing that, in the event of a S...leak from the pipeline resulting in the generation of a first acoustic signal, the S.....transmission of a second acoustic signal along the pipeline by way of the wave guide would result in the generation of a characteristic interference signal detectable at a predetermined location remote from the leak.6 A pipeline as claimed in Claim 4 including a pipeline wall through which a first fluid is displaced and the pipeline acts to separate the first fluid from a second fluid outside the pipeline.7 A pipeline as claimed in Claim 4 or Claim 5 wherein the first fluid is a liquid and the second fluid is a liquid of different composition to the first fluid.8 A pipeline as claimed in Claim 4 or Claim 5 wherein the first fluid is a liquid and the second fluid is a gas or vapour or a mixture including a gas and a vapour.9 A method of leak detection as hereinbefore described with reference to Figures 1(a) to 1(c) of the accompanying drawings.A pipeline as hereinbefore described with reference to Figures 2 and 3 of the accompanying drawings. * . * . * * ** * S.. * * *.** * * * I. *S S.. * S.. * S * *. a* SS S. S * S