GB2506837A

GB2506837A - A method of identifying leaks in a fluid carrying conduit

Info

Publication number: GB2506837A
Application number: GB1214104.0A
Authority: GB
Inventors: Andrew Hoffman
Original assignee: Atmos Wave Ltd
Current assignee: Atmos Wave Ltd
Priority date: 2012-08-07
Filing date: 2012-08-07
Publication date: 2014-04-16
Anticipated expiration: 2032-08-07
Also published as: GB2506837B; GB201214104D0

Abstract

A method of determining the presence and/or the location of one or more leaks in a pipeline for carrying fluids, the method comprising the steps of: at least partially blocking a first point 301 on the pipeline 300; monitoring fluid pressure in the pipeline at a second point 302 on the pipeline for a time period; and processing the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first and second points. Advantageously, the method according to the present invention does not require the fluid pressure to be monitored at both ends of the pipeline, and, in contrast to leak detection methods which monitor fluid pressure at two points on a pipeline, it does not require an accurate timing mechanism to ensure that the two measurements are substantially simultaneous. Also disclosed is apparatus for carrying out the method.

Description

A method of identifying leaks in a fluid carrying conduit The present invention relates to a method of determining whether or not there is a leak in a pipeline for carrying fluids. In particular, but not exclusively, it relates to the detection of leaks in hydrant systems.

It is often necessary to convey fluids such as water and oil from a first place to a second place where the fluid is required. Often, the fluid may be conveyed to one or more tanks and stored therein for later use. The tank may be connected to one or more sources of fluid via a dedicated system of pipes so that the fluid in the tank can be replenished. Alternatively, fluid may be transported to the tank by some other means, such as by rail or by road. Fluid can be pumped from the tank to a desired location as desired.

For example, airports are often provided with one or more dedicated tanks to store fuel for aircrafts. When an aircraft requires fuel, the fuel can be pumped to from the tank via a hydrant system. The hydrant system comprises one or more pipelines, or hydrants, with a first end of each hydrant being connected to the tank and the second end of the hydrant being connectabie to an aircraft and controlled by a valve. The system may contain fluid under pressure and, once the second end of a hydrant is connected to an aircraft, the flow of fuel from the hydrant system to the aircraft may be controlled simply by the valve.

Pipelines, such as hydrant systems, are susceptible to leaks where the walls of the pipelines are breached. It is important that such leaks or thefts be identified and located as quickly as possible so as to reduce the amount of fluid lost. Furthermore, in the case of an accidental leak of a fluid such as oil, early detection can help minimise the environmental impact of the leak and the risk of fire that such a flammable fluid poses. Therefore there is a need for a method of accurately and reliably determining and locating leaks or thefts in pipelines. At least part of a hydrant system may be inaccessible, for example it may be disposed underground, and therefore it is desirable that said method detects leaks remotely.

When a leak develops in a pipeline the line fluid pressure in a section of the pipeline near to the leak will drop. The initial pressure drop is a dynamic effect caused by the inability of the fluid to respond instantly to the leak. After this initial pressure drop, the pressure continues to drop at a slower rate due to unpacking of the pipeline. Such a pressure drop gives rise to a rarefaction wave. The rarefaction wave starts as a spherical wave centred on the location of the leak. As the rarefaction wave propagates away from the location of the leak it interacts with the pipe wall and changes shape, eventually giving rise to two plane waves each of which propagates down the pipe, in opposite directions, at the speed of sound. By measuring the pressure f the fluid at two positions which are on opposite sides of the leak, these pressure waves can be detected and used to infer the presence of a leak and the position thereof. Two such methods are disclosed in US 5,388455 and WO 2011/070343.

Another known method of determining whether or not there is a leak in a pipeline is to close off both ends of the pipeline and to monitor the pressure over a period of time. The pressure may drop over time if either there is a leak or if the temperature of the fluid in the pipeline differs from that of the ambient temperature surrounding the pipeline. The shape of the pressure curve as a function of time is different for each of these two scenarios and can therefore be used to distinguish between them. However, the pipeline must be closed off for a significant time period, typically several hours, before one can distinguish between the two scenarios and determine whether or not there is a leak. This is inconvenient and can be costly. Furthermore, even if this method concludes that there is a leak in the pipeline does not yield any information regarding its location.

It is an object of embodiments of the present invention to provide an alternative, improved method of determining the presence of leaks in pipelines.

According to a first aspect of the present invention there is provided a method of determining the presence and/or the location of one or more leaks in a pipeline for carrying fluids, the method comprising the steps of: at least partially blocking a first point on the pipeline; monitoring fluid pressure in the pipeline at a second point on the pipeline for a time period; and processing the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first and second points.

Any leaks in the pipeline between the first and second points will give rise to two rarefaction waves propagating in opposite directions: one towards the first point and the other towards the second point. The method utilises the fact that when the first point is at least partially blocked, any rarefaction waves which propagate towards the first point will be reflected back S towards the second point. Therefore, both waves will arrive at the second point but at different times. Therefore, by processing the fluid pressure in the pipeline as measured at the same point but at different times, the presence and/or location of leaks can be inferred.

Advantageously, the method according to the present invention does not require the fluid pressure to be monitored at both ends of the pipeline. Furthermore, in contrast to leak detection methods which monitor fluid pressure at two points on a pipeline, the method according to the present invention does not require an accurate timing mechanism, such as OPS timing, to ensure that the two measurements are substantially simultaneous.

The fluid pressure may be measured using a pressure sensing means. Preferably, a pressure sensing means which results in low noise is chosen. More specifically, the noise may be separated into two categories: ordinary noise which is a result of natural local pressure fluctuation, for example as a result of turbulent fluid flow, and quantisation noise which is a result of the finite rate at which the data is sampled. It is especially desirable to choose a pressure sensing means which results in a low level of quantization noise. The pressure sensing means may cOmprise any or all of the following: pressure sensors, microphones andstrain gauges. The fluid pressure may be measured directly or indirectly. For example, the fluid pressure may be measured by a pressure sensor in contact with the fluid in the pipeline. Alternatively, the pressure sensor may comprise a microphone disposed outside of, but close to, the fluid in the pipeline.

Preferably, the first point is chosen to be proximate to a first end of a section of the pipeline which it is desirable to monitor, and the second point is chosen to be proximate to the other, second, end of that section of the pipeline.

The method may further comprise the steps of monitoring fluid pressure in the pipeline at one or more additional points on the pipeline for a time period; and processing the fluid pressure as measured at each additional point a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first point and each additional point. The one or more additional points may be disposed close to the second point.

The step of at least partially blocking the first point on the pipeline preferably blocks the first point sufficiently so as to produce a sufficiently strong reflection so as to be measurable at the second point given the attenuation of pressure waves in the pipeline. Preferably, the first point on the pipeline is completely, or substantially completely, blocked. The first point on the pipeline may comprise a valve and may be blocked by closing said valve.

The fluid pressure in the pipeline at a second point may be monitored continuously or substantially continuously during the time period.

The method may be employed during a hydrostatic test. To this end both the first and second points on the ppe1ne may be comptaly, or substantially completely, blocked and the fluid in the pipeline may be pressurised. Said pressurisation may be to any pressure as is desired or required and said pressure may exceed normal operating pressures for the pipeline.

The pipeline may form part of a hydrant system. The hydrant system may comprise an inletend with a single pressure sensor and a plurality of outlets, each of which comprises a sealing valve. The hydrant system may comprise a main pipeline running between the inlet end and an end outlet. A plurality of branches may each run off the main pipeline to a different outlet.

In addition to the fluid pressure as measured at the first and second times, the fluid pressure as measured at one or more additional times may also be processed to infer the presence and/or location of a leak in the pipeline. Advantageously, this may allow the method to be applied in situations where there is potentially a plurality of sources of reflections. For example, this may be useful for the use of the method as applied to a hydrant system.

The method may be used for pipelines carrying any fluid including, but not limited to water, oil and derivatives thereof.

The difference between the first and second times may be substantially equal to the time of flight for a pressure wave in the fluid to propagate between the first and second points. That is to say the difference between the first and second times may be substantially equal to the ratio of the distance between the first and second points to the speed of sound in the fluid. This is the time taken for a reflection to propagate from the first point to the second point. For such embodiments, at least a component of the pressure measured at the second point at the second time will correspond to the pressure that would have been measured at the first point at the first time had there been a pressure sensor at the first point. Therefore by processing this with the pressure measured at the second point at the first time, one is effectively processing the simultaneous pressure at the two points on the pipeline. Advantageously, this information can therefore be fed directly into a prior art leak detection method which takes as its input the simultaneous pressure at the two points on the pipeline.

Therefpre, the step of processing the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline may

comprise the step using such a prior art method.

For example, the step of processing the fluid pressure as measured at a first time with that as measured at a second time to inter the presence and/or location of a leak in the pipeline may comprise the step of using the method disclosed in WO 2011/070343. Additionally or alternatively, any other method of monitoring the presence and/or location of a leak, such as the method disclosed in US 5,388,455, may be used.

The method disclosed in WO 2011/070343 essentially combines the simultaneously monitored fluid pressure at two points on the pipeline to form a two dimensional probability distribution. In the present invention, the simultaneously monitored fluid pressures at two points on the pipeline are replaced by the pressure measured at the same point at the first and second times. The two dimensional probability distribution can be used to locate any sources of pressure waves such as leaks in the pipeline.

In more detail, the method according to the present invention may comprise the steps of: determining first and second quantities, being related to a differential with respect to time of the two input fluid pressures; combining the first and second quantities to produce a two dimensional intensity function of time and a position variable, and analysing the magnitude of the intensity function to derive information relating to the fluid. The first quantity may be related to a differential with respect to time of the fluid pressure as measured at the first time and the second quantity may be related to a differential with respect to time of the fluid pressure as measured at the second time.

The first and second quantities may be related to the second time derivative of the two fluid pressures. For example, the first and second quantities may be proportional to the second differential with respect to time of the two fluid pressures respectively.

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algorithm. Before the second differentials with respect to time of the fluid pressure at the first and second times are determined using the numerical estimate algorithm, the raw data may be smoothed, This avbids the complication that the output of numerical estimates of second differentials for noisy input data is typically unreliable. Preferably, the raw data is smoothed by performing a local time averaging. In a preferred embodiment, a second data set is.found from each of the raw data sets, wherein a point in the first data set proportional to the average of h corresponding data points in the raw data set. This second data set is substantially smoother than the raw data and is therefore a more suitable input to the numerical estimate algorithm. In a particularly preferred embodiment, the raw data is sampled at a high rate, for example at a rate of the order of 100 Hz. By choosing a high sampling rate for the raw data, the second data set retains adequate temporal resolution despite the averaging.

Preferably, the position variable corresponds to the displacement of points, on the pipeline relative to a fixed origin point, that is the displacement possesses both magnitude and direction and, as such, it can be positive or negative. For example, the fixed origin point may be a point on.the pipeline midway between the first point and the second point. Preferably, the position variable is converted into units of time using the speed of propagation of pressure waves through the fluid in the pipeline. By doing this the position variable so formed, p, corresponds to S the time of flight of a pressure wavefrom points on the pipeline to the fixed origin point.

The intensity function may be produced by combining the first and second quantities in such a way that correlations between the first and second quantities correspond to local maxima and/or minima of the intensity function.

The first and second quantities, A and B respectively, are functions of time, that is A=A(t) and B=B(t). Preferably, for a fixed value of time, t, and position variable (in units of time), p, the intensity function is found by combining a region of the first quantity centred on t+p with a region of the second quantity centred on t-p. The size of the regions may be chosen to be 2x, where x corresponds to a time greater than the time of flight of a pressure wave propagating from the first point on the pipeline to the second point. For example, x may be approximately 125% of the time of flight of a pressure wave propagating from the first point to the second point.

In a particularly preferred embodiment, the intensity function is given by: fl=p+x I(t,p) = A(t-n)B(t+n), (1) where A and B are the first and second quantities respectively, t is the time and p is the position variable in units of time.

The method may further comprise the steps of: determining whether or not the magnitude of the intensity function satisfies pre-determined criteria and, if the intensity function does satisfy the pre-determined criteria, concluding that a leak is present. This works because the intensity function essentially represents a substantially continuous probability function, wherein its absolute value is related to the probability of a leak having occurred.

The pre-deterniiried criteria may comprise requiring a local minimum or maximum of the intensity function. This may be found by any suitable method, for example using a numerical estimate to find the total differential of the intensity function and requiring this to be below a pre-set threshold value, using an iterative method or by any other method as is desired.

The may further comprise the step of identifying all local maxima and arranging these in ascending order. In such embodiments each of these maxima maybe a potential leak candidate.

Preferably, the method further comprises the step of comparing all leak candidates which correspond to a maximum with a pre-set threshold value. The method may further comprise the step of rejecting all candidates corresponding to a maximum which is below the pre-set threshold.

The method may comprise the step of rejecting any leak candidates which correspond to maxima which are close to a larger maximum. In this way for a cluster of adjacent maxima, only the largest is considered. For embodiments comprising this step, two maxima may be determined to be close if the distance between them is smaller than a pre-set threshold.

Furthermore, the distance may be a spatial distance, a temporal distance, a distance between the two maxima in the t-p plane or any combination of these as desired and/or required. In a particularly preferred embodiment, the step of rejecting any leak candidates which correspond to maxima which are close to a larger maxima may comprise the sub-steps of: determining whether or not the two peaks are temporally separated by more than a pre-set temporal separation threshold, checking that the ratio of the smaller peak intensity to the larger peak intensity is above a pre-set intensity threshold, and checking that the two peaks are spatially separated by more than a pre-set spatial threshold. In such embodiments the smaller peak is only considered to be a leak candidate if all of these criteria are met. Alternatively, the smaller peak may be considered to be a leak candidate if two of these criteria are met.

The first and second points on the pipeline correspond to two lines in the t-p plane in which the, intensity function is defined and the central region between those two lines corresponds to the continuum of points on the pipeline between the first and second points. The method may further comprise the step of rejecting any leak candidates which correspond to maxima lying outside of the central region. This is particularly advantageous as it leads to the rejection of transient waves propagating along the conduit. Therefore, any pressure wave whose source is not between the first and second points, for example as a result of the pipe receiving an external blow, will not lead to false determination of leaks in the conduit. Furthermore, for a scenario wherein the pipeline has a leak between the first and second points, the method of the present invention will typically lead to a plurality of peaks in the intensity function: one peak in the central region which is indicative of the leak and one or more peaks on the edge of the central region. By only considering the peak in the central region, the true location of the leak can be identified.

The method may further comprise the step of rejecting some or all of the candidates which correspond to maxima which are arranged in a straight line in the t-p plane. This rejection may only be applied for arrangements wherein the absolute value of the gradient of the line is substantially the same as the speed of propagation of pressure waves through the fluid. This is particularly advantageous since it allows for rejection of large packing transient waves. A pipeline which carries a fluid may comprise: a pump at one end of the pipeline operable to pump the tiuid towards the other end of the pipeline; and a valve at the other end of the pipeline operable to restrict the flow of fluid out of the other end of the pipeline. Therefore, when the pipeline does not contain the desired quantity of the fluid, the pipeline may be packed' by operating the pump while closing the valve to restrict the fluid flow out of the pipeline. This will result in an increase in the quantity of fluid inside the pipeline and, therefore, will result in an overall increase in the fluid pressure; Such increases in fluid pressure as a result of packing the pipe, or corresponding decreases in fluid pressure as a result of draining the pipe, can lead to candidates which correspond to maxima which are arranded in a straight line in the t-p plane wherein the absolute value of the gradient of the line is substantially the same as the speed of propagation of pressure waves through the fluid. Therefore by rejecting such leak candidates false alarms may be reduced Furthermore, it allows for a correct treatment of leaks occurring while the fluid pressure is altered externally.

Preferably, the method further comprises the step of determining the ratio of leak transients. When a leak occurs in the region of the pipeline in between the first point and the second point, two pressure waves will propagate along the pipeline, in opposite directions. As such, the pressure sensing means will measure a pressure change at the second point at two different times, one corresponding to the pressure wave propagating towards the second point and the other corresponding to the reflection of the pressure wave that propagated in the opposite direction. There iill therefore be corresponding maxima and/or minima in the first and second quantities. Since the pressure wave which is reflected travels farther than the other pressure wave, one would expect the intensity of the maximum in the first quantity, I, to be larger than the maximum in the second quantity, 2. Leak candidates result from the combination of a region of the first quantity containing a peak being combined with a region of the second quantity containing another peak. If the attenuation of pressure waves along the pipeline is known, then given the position of a leak candidate, the intensities of the peaks in the first and second quantities from which it was found may be used to reject false leak candidates. This shall be referred to hereinafter as determining the ratio of leak transients. For example, say the distance between the leak and the second point is, L1, the distance between the leak and the first point is, 1.., and the distance between the first and second points s, L= L1+L2, by assuming that the attenuation of pressure waves is a linear function of distance travelled, one would expect the ratio of 11xL1 to 12x(L2+L) to be approximately 1. In a preferred embodiment of the present invention, the step of determining the ratio of leak transients may compilsS requiring the ratio of 11,cL1 to 12x(L2+L) to be approximately 1. This step of determining the ratio of leak transients may take into account any attenuation of a pressure wave as it is reflected from the first point on the pipeline.

If the transmission loss of the pipe is known then ghost peaks, which are generated as a result of leaks occurring concurrently with line packing, may be rejected.

The method may further comprise the step of rejecting a group of candidates if they correspond to a group of maxima occurring at substantially the same time, Preferably, such rejection occurs only if the number of peaks occurring at substantially the same time is greater than a pie-determined value. This is particularly advantageous because when the operational conditions of the fluid are altered substantially, false maxima, which do not correspond to leaks, may be generated. Typically these false maxima are generated at substantially the same time.

The method may comprise the step of summing all peak candidates which correspond to the same position on the conduit, whether they are above or below the pre-set threshold, over an extended time period. Advantageously, this enables several small leaks or thefts of fluid from the same location on the conduit, which may otherwise go unnoticed, to be discovered.

Preferably a distribution is formed by summing all peak candidates which correspond to the same position on the conduit. The distribution may be a histogram which is filled by making a list of all leak candidates in the two dimensional intensity function and for each leak candidate: determining the position value of each peak in the list and incrementing the value of the bin of the histogram within which that position value falls. The histogram may be filled in a weighted or unweighted manner. For an unweighted histogram, the bin may be incremented by one for each candidate, whereas for a weighted histogram the bin may be incremented by a quantity which is related to the intensity of the each candidate. For example, the quantity may be proportional to the intensity of the candidate, The bins of the histogram may be chosen to be of any suitable size.

The method may further comprise the step of determining the location of a leak in the pipeline by: identifying the position of the leak by mapping the location of the region of the intensity function which satisfies the pie-determined criteria onto a corresponding position on the pipeline.

The method may further comprise the steps of: analysing the two dimensional intensity function to produce a distribution which is related to the density of peaks as a function of the position variable; and analysing the distribution to determine the speed of the pressure waves.

According to a second aspect of the present invention there is provided an apparatus suitable for determining the presence andfor location of one or more leaks in a pipeline for carrying fluids, said apparatus comprising: a means for at least partially blocking a first point on the pipeline; a means for monitoring fluid pressure at a second point on the pipeline; and a processing means characterised in that the processing means is operable to process the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first and second points.

The apparatus according to the second aspect of the present invention may comprise any or all features of the method according to the first aspect of the present invention as desired or required.

In order that the invention may be more clearly understood an embodiment thereof will now be described, by way of example only, with reference to the accompanying drawings, of which: Fig. I is a schematic representation of a prior art arrangement utilising two pressure sensors; Fig. 2 shows the temporal location of the rarefaction wave fronts which would be measured by the two pressure sensors of the apparatus shown in Fig. 1 when both ends of the pipeline are sealed and there is a single leak disposed therebetween; and Fig. 3 is a schematic representation of a hydrant system comprising a single pressure sensor and which is suitable for implementing a method of leak detection according to the present invention.

Referring to Fig. 1, a prior art arrangement is shown. A first pressure sensor Ill is disposedat a first point 101 on a fluid carrying pipeline lop and a second pressure sensor 112 is disposed at a second point 102 on the pipeline 100. The first and second points 101, 102 are separated bya distance L. The pressure of fluid in the pipeline 100 is monitored and, in the event of a leak in the pipeline 100, two rarefaction waves will propagate through the fluid in the pipeline in opposite directions away from the location of the leak, The two pressure sensors 101, 102 can detect these two rarefaction waves, which can be used to infer the presence, and the position, of a leak using a method such as those disclosed in US 5,388,455 and WO 2011/070343.

In the example shown in Fig.1, the pipeline 100 has a leak 103 which is disposed at a distance x from the first pressure sensor 111. Referring now to Fig. 2, the temporal positions of the rarefaction wavefronts measured by each of the two pressure sensors are shown when the pipeline 100 is shut in' by sealing the pipeline at the first and second points 101 102. If the leak S occurs at t0, then a first one of the rarefaction waves will reach the first pressure sensor 111 at a 1-xiv, where v is the speed of Sound in the fluid in the pipeline 100, as indicated by 210.

Similarly, the second rarefaction wave will reach the second pressure sensor 112 at a L-(L-x)iv, as indicated by 220.

Since the pipeline 100 is shut in, the first the rarefaction wave be reflected at the first end 101 and the reflection will reach the second pressure sensor 112 at a l-(x+L)iv, as indicated by 221. Similarly, the second wave will be reflected at the second end. 102 and the reflection will reach the first pressure sensor 111 at a t-(2L-x)iv, as indicated by 211. The two waves will continue to propagate between the first and second ends 101, 102 although the magnitude of the wave fronts will diminish due to attenuation of the waves in the fluid. A second reflection of the first wave will reach the first pressure sensor 111 at a r-(x+2L)Iv, as indicated by 212 and a second reflection of the second wave will reach the second pressure sensor 112 at a fr-(3L-x)Iv, as indicated by 222.

The method according to the present invention utilises the fact that the reflection of one of the waves from the end towthrds which it propâgãtes will reach the apposite end a time LI v later. For example, the first wave 211 will reach the first end 101 at a time 210 whereas the first reflection of the first wave 211 will reach the second end 102 at a time 221 which s Liv later.

Therefore, at least a component of the pressure measured at the second point 102 at a later time will correspond to the pressure that would have been measured at the first point 101 at an earlier time.

A method of determining the location of one or more leaks in a pipeline for carrying fluids according to the present invention comprises the steps of: at least partially blocking a first point 101 on the pipeline 100; monitoring fluid pressure in the pipeline at a second point 102 on the pipeline 100 for a time period; and processing the fluid pressure as measured at a first time 220 with that as measured at a second time 221 to infer the presence and/or location of a leak in the pipeline 100 between the first and second points 101, 102.

Advantageously the method according to the present invention does not require the fluid pressure to be monitored at both ends 101, 102 of the pipeline. Furthermore, in contrast to leak S detection methods which monitor fluid pressure at two points on a pipeline, the method according to the present invention does not require an accurate timing mechanism such as OPS timing, to ensure that the two measurements are substantially simultaneous.

The step of processing the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline may comprise the step using a prior art method. Preferably, the method disclosed in WO 20111070343 is used. The method disclosed in WO 2011/070343 essentially combines the simultaneously monitored fluid pressure at two points on the pipeline to form a two dimensional probability distribution. In the present invention, the simultaneously monitored fluid pressures at two points on the pipeline are replaced by the pressure measured at the same point at the first and second times. The two dimensional probability distribution can be used to locate any sources of pressure waves such as leaks in the pipeline.

As explained above, with reference to Figs. I & 2, the difference between the first and second times may be substantially equal to the time of flight for a pressure wave in the fluid to propagate between the first and second points. That is to say the difference between the first and second times may be substantially equal to the ratio of the distance between the first and second points to the speed of sound in the fluid, Liv. At least a component of the pressure measured at the second point at the second time will correspond to the pressure that would have been measured at the first point at the first time had there been a pressure sensor at the first point.

Therefore by processing this with the pressure measured at the second point at the first time, one is effectively processing the simultaneous pressure at the two points on the pipeline and, advantageously, this information can therefore be fed directly into a prior art leak detection method which takes as its input the simultaneous pressure at the two points on the pipeline.

Additionally or alternatively, the pipeline may form part of a hydrant system 300, as shown in Fig. 3. The hydrant system comprises an inlet end 301 with a single pressure sensor 311 which is connected to a plurality of outlets 302a-302d, each of which comprises a sealing valve. The hydrant system 300 comprises a main pipeline 320 running between the inlet end 301 and an end outlet 302d. A plurality of short branches 321, 322, 323 run off the main pipeline 320 to a different outlet 302a-302c.

With such a hydrant system 300, the difference between the first and second times may be substantially equal to the time of flight for a pressure wave in the fluid to propagate between the end outlet 302d and the inlet point 301. However, as will be obvious to one skilled in the art, the method may be altered to take account for the fact that there are potentially several sources of reflections with such a hydrant system.

The above embodiment is described by way of example only. Many variations are possible without departing from the scope of the invention as defined in the appended claims.

Claims

CLAIMS1. A method of determining the presence and/or the location of one or more leaks in a pipeline for carrying fluids, the method comprising the steps of: at least partially blocking a first point on the pipeline; monitoring fluid pressure in the pipeline at a second point on the pipeline for a time period; and processing the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first and second points.
2. A method as claimed in claim 1, wherein the fluid pressure is monitored directly.
3. A method as claimed in claim 1, wherein the fluid pressure is monitored indirectly.
4. A method as claimed in any preceding claim, further comprising the steps of: monitoring fluid pressure in the pipeline at one or more additional points on the pipeline for a time co period; and processing the fluid pressure as measured at each additional point a first v" time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first point and each additional point.

LCD
5. A method as claimed in any preceding claim, wherein the step of at least partially O blocking the first point on the pipeline, blocks the first point sufficiently so as to produce a sufficiently strong reflection so as to be measurable at the second point, given the attenuation of pressure waves in the pipeline.
6. A method as claimed in any preceding claim, further comprising the step of substantially completely blocking the first point on the pipeline.
7. A method as claimed in any preceding claim, further comprising the step of at least partially blocking the second point on the pipeline.
8. A method as claimed in claim 7, wherein the second point on the pipeline is substantially completely blocked.
9. A method as claimed in claim 8, when dependent directly or indirectly on claim 6, comprising a further step of pressurising the fluid in the pipeline.
10. A method as claimed in any preceding claim, wherein the step of at least partially blocking a point on the pipeline is carried out by closing a valve located in the pipeline.
11. A method as claimed in any preceding claim, wherein the fluid pressure is continuously monitored.
12. A method as claimed in any preceding claim, further comprising the step of measuring the fluid pressure at one or more points on the pipeline
13. A method as claimed in any preceding claim, further comprising the step of measuring the fluid pressure at two or more additional times.
14. A method as claimed in any preceding claim, further comprising the steps of: determining first and second quantities, being related to a differential with respect to time of the two input fluid pressures; combining the first and second quantities to produce a two dimensional intensity function of time and a position variable, and analysing the C') magnitude of the intensity function to derive information relating to the fluid in order to locate any sources of pressure waves such as leaks in the pipeline.0
15. A method as claimed in claim 14, wherein the first quantity is related to a differential with LI') respect to time of the fluid pressure as measured at the first time and the second quantity is related to a differential with respect to time of the fluid pressure as measured at the second time.
16. A method as claimed in either of claims 14 or 15, wherein the first quantity is related to a second differential with respect to time of the fluid pressure as measured at the first time and the second quantity is related to a second differential with respect to time of the fluid pressure as measured at the second time.
17. A method as claimed in either of claims 15 or 16, further comprising the step of smoothing the raw data.
18. A method as claimed in any of claims 15 to 17, further comprising the step of determining the first and second quantities using suitable numerical estimate algorithms.
19. A method as claimed in any of claims 14 to 18, wherein the position variable corresponds to the displacement of points on the pipeline relative to a fixed origin point.
20. A method as claimed in any of claims 14 to 19, wherein the position variable is converted into units of time using the speed of propagation of pressure waves through the fluid in the pipeline.
21. A method as claimed in any of claims 14 to 20, further comprising the step of producing an intensity function by combining the first and second quantities in such a way that correlations between the first and second quantities correspond to local maxima and/or minima of the intensity function.
22. A method as claimed in claim 21, further comprising the steps of: determining whether or not the magnitude of the intensity function satisfies pre-determined criteria and, if the intensity function does satisfy the pre-determined criteria, concluding that a leak is Ct) present.
23. A method as claimed in claim 22, wherein the pre-determined criteria comprise requiring 0 a local minimum or maximum of the intensity function and identifying such maxima or LI') minima as leak candidates.
24. A method as claimed in claim 23, wherein the local minima and maxima are found using a numerical estimate to find the total differential of the intensity function and requiring this to be below a pre-set threshold value.
25. A method as claimed in any of claims 22 to 24, further comprising the step of identifying all local maxima and arranging these in ascending order.
26. A method as claimed in claim 25, further comprising the step of comparing all leak candidates which correspond to a maximum with a pre-set threshold value and rejecting all candidates corresponding to a maximum which is below the pre-set threshold.
27. A method as claimed in any of claims 22 to 26, further comprising the step of rejecting any leak candidates which correspond to maxima which are close to a larger maximum.
28. A method as claimed in claim 27, wherein the step of rejecting any leak candidates which correspond to maxima which are close to a larger maxima comprises the sub-steps of: determining whether or not the two peaks are temporally separated by more than a pre-set temporal separation threshold, checking that the ratio of the smaller peak intensity to the larger peak intensity is above a pre-set intensity threshold, and checking that the two peaks are spatially separated by more than a pre-set spatial threshold.
29. A method as claimed in any of claims 22 to 28, further comprising the step of rejecting any leak candidates which correspond to maxima lying outside of a central region defined by the first and second positions.
30. A method as claimed in any of claims 22 to 29, further comprising the step of rejecting some or all of the candidates which correspond to maxima which are arranged in a straight line in the time/position variable plane.C')
31. A method as claimed in claim 30 wherein this rejection is only be applied for arrangements wherein the absolute value of the gradient of the line is substantially the C same as the speed of propagation of pressure waves through the fluid.LU
32. A method as claimed in any of claims 22 to 31 further comprising the step of determining the ratio of leak transients.
33. A method as claimed in claim 32, wherein the step of determining the ratio of leak transients may comprise requiring the ratio of!1xL1 to /2x(L2+L) to be approximately 1, where! and /2, are maxima in the first and second quantities respectively, and L1,and L2 are the distances from the leak candidate position to the second and first points respectively.
34. A method as claimed in any of claims 22 to 33, further comprising the step of rejecting ghost peaks, which are generated as a result of leaks occurring concurrently with line packing.
35. A method as claimed in any of claims 22 to 34, further comprising the step of rejecting a group of candidates if they correspond to a group of maxima occurring at substantially the same time.
36. A method as claimed in any of claims 22 to 35, further comprising the step of summing all peak candidates which correspond to the same position on the conduit over an extended time period.
37. A method as claimed in claim 36 wherein a distribution is formed by summing all peak candidates which correspond to the same position on the conduit.
38. A method as claimed in claim 37, the method further comprising the step of determining the location of a leak in the pipeline by: identifying the position of the leak by mapping the location of the region of the intensity function which satisfies the pre-determined criteria onto a corresponding position on the pipeline.CO
39. A method of determining the speed of pressure waves propagating through a fluid flowing in a fluid carrying conduit comprising the steps of: monitoring the fluid flow in the fluid C carrying conduit in accordance with a method as claimed in any one of claims 1 to 20; LI') analysing the two dimensional intensity function to produce a distribution which is related to the density of peaks as a function of the position variable; and analysing the distribution to determine the speed of the pressure waves.
40. An apparatus suitable for determining the presence and/or location of one or more leaks in a pipeline for carrying fluids, said apparatus comprising: a means for at least partially blocking a first point on the pipeline; a means for monitoring fluid pressure at a second point on the pipeline; and a processing means characterised in that the processing means is operable to process the fluid pressure as measured at a first time with that as measured at a second time to infer the presence and/or location of a leak in the pipeline between the first and second points.
41. An apparatus as claimed in claim 40, wherein the fluid pressure is monitored by a pressure sensing means.
42. An apparatus as claimed in claim 41, wherein the pressure sensing means is in direct contact with the fluid in the pipeline.
43. An apparatus as claimed in claim 41, wherein the pressure sensing means is disposed outside of the pipeline, but close to the fluid in the pipeline.
44. An apparatus as claimed in any of claims 41 to 43, wherein the pressure sensing means produces a low level noise output.
45. An apparatus as claimed in claim 44, wherein the pressure sensing means results in a low level output of quantisation noise.
46. An apparatus as claimed in any of claims 41 to 45, wherein the pressure sensing means may comprise any or all of the following: pressure sensors, microphones and strain gauges.
47. An apparatus as claimed in any preceding claim wherein the pipeline forms part of a hydrant system.o
48. An apparatus as claimed in any preceding claim wherein the pipeline carries any one or LU all of water, oil and derivatives thereof.
49. An apparatus as claimed in any preceding claim comprising any or all of the features of the method according to any of claims ito 38.
50. A method substantially as herein described with reference to any of the accompanying drawings.
51. An apparatus substantially as herein described with reference to any of the accompanying drawings.