Measuring and testing – With fluid pressure – Leakage
Reexamination Certificate
2001-01-30
2003-03-11
Williams, Hezron (Department: 2856)
Measuring and testing
With fluid pressure
Leakage
C073S04050A, C073S592000
Reexamination Certificate
active
06530263
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates generally to methods and apparati for detecting leaks in fluid conveying conduits, and more particularly to methods and apparati for detecting and accurately locating the position of leaks in fluid conveying conduits which are buried underground or otherwise inaccessible for inspection.
Fluid conveying conduits, such as water distribution pipelines, commonly experience leaks. To complicate matters, because fluid conveying conduits are commonly buried underground or are otherwise unexposed or inaccessible, leaks produced by such conduits often do not surface and, therefore, are not detected. As a result, fluid conveying conduits can often experience leaks for prolonged periods of time, such one or more years, without ever being detected, which is highly undesirable.
Accordingly, a multi-stage inspection process is commonly performed in the art to localize and correlate leaks in fluid conveying conduits.
Specifically, in the primary stage, a general surveying, or localization, mode is commonly executed to determine the presence of leaks in a conduit, such as a pipeline. Leak localization is commonly achieved by monitoring the flow of the fluid into and out of a district metered area (DMA), by monitoring minimum night flow of the fluid, or by utilizing sound loggers to detect when the noise produced by the fluid exceeds a pre-determined threshold.
In the secondary stage, a more detailed correlation mode is commonly executed to determine the exact location of the leaks in the underground fluid conveying conduit. Specifically, correlators are commonly used on the surface above an underground pipeline or directly upon an easily accessible, external device, such as a valve or hydrant, in order to more accurately determine the position of leaks in the conduit. After correlators are used to determine the position of the leaks, the ground directly above the leaks is excavated so that the leaks can be repaired. As can be appreciated, by knowing the exact location of the leaks in the conduit, excavation can be limited to only the portion of the street surface which is directly above the leaks, thereby reducing excavation costs and repair time, which is highly desirable.
Correlators commonly utilize sound technology to determine the location of leaks. Specifically, it is well known that a fluid, such as water, which escapes from a pressurized conduit, such as a pipeline, produces a high frequency sound wave that is propagated along the conduit with a constant velocity in both directions away from the source of the leak. It is also well known that, by placing a pair of sensors on opposite sides of the leak, the leak noise will be received at the sensors at different times depending upon the distance of each sensor from the source of the leak. Since the propagating velocity of the sound wave can be easily calculated, the location of the leak in the pipeline can be determined as a function of the time difference in which each sensor detects the sound wave.
In U.S. Pat. No. 4,083,229 to A. R. Anway, there is disclosed a method and apparatus for detecting and locating a fluid leak in an underground pipe or the like in which the vibration produced by the leak is intercepted at selected spaced apart points by microphones or other transducers, in which the vibration intercepted at each of the two points in converted into an electrical signal, and in which the extent of correlation of the two resulting signals is varied by variably time delaying one signal relative to the other to determine the leak's location fro the occurrence of maximum correlation between the signals. In one embodiment, the variable time delay of one signal relative to the other is accomplished by a variable length time delay line and a means for progressively varying the length of the delay line. In another embodiment, the variable time delay is accomplished by a recirculating delay line analyzer that does more data age comparisons with the same delays in the same time than the variable length delay line.
The method and apparatus for detecting and locating a fluid leak in an underground pipe disclosed in the aforementioned patent to Anway utilizes a cross-correlation measurement technique in which one signal is progressively delayed relative to the other while the apparatus continues to compare the similarity between the two signals. This enables the device to measure the difference in travel time T
d
of the leak noise to the respective sensors. By determining the velocity of sound for the particular pipeline and knowing the distance between the sensors, the apparatus can compute the leak position in accordance with the following formula:
L=[D−
(
V×T
d
)]/2
where L is the leak position relative to one sensor, D is the overall distance between the sensors, V is the velocity of sound in the pipeline medium, and T
d
is the transit time difference.
In U.S. Pat. No. 5,205,173 to T. J. Allen, there is disclosed an improved method and apparatus for detecting leaks in pipelines using cross-correlation techniques including improved correlating circuitry featuring a pair of circulating delay lines for respectively receiving, temporarily storing and processing in a revolving sequence, samples of input data obtained from a pair of remotely positioned sensors, a multiplying circuit for causing samples input to each channel to be multiplied by each sample stored in the circulating delay line associated with the other channel, an adder and accumulator memory for accumulating the multiplication results, and a display for displaying the correlation results.
Although well known and widely used in commerce, prior art methods and apparati for detecting and locating fluid leaks in underground conduits suffer from notable drawbacks.
As an example, prior art methods and apparati for detecting and locating fluid leaks in underground conduits typically need to analyze the sound data obtained by the pair of sensors in real time. Specifically, the sound data detected by the sensors is transmitted to a central correlating unit via a communications link, such as radio or hard wire links. The data transmitted to the central correlating unit is then analyzed in real time by a correlation workforce, the real time analysis ensuring that the sound data detected by the sensors is synchronized in time. As a result, because the sound data must be analyzed in real time, the data can not be used in repeat correlations or comparisons after repair work has been carried out on the site of the leaks. In addition, because the sound data must be analyzed in real time, a constant correlation workforce is required during the accumulation of sound data by the sensors, thereby increasing expenses and operation time, which is highly undesirable.
As another example, although well known and widely used in commerce, the conventional multi-stage inspection process described above for localizing and correlating leaks in fluid conveying conduits is typically accomplished using different equipment and different workforces, thereby increasing equipment and labor costs, which is highly undesirable.
As another example, prior art methods and apparati for detecting and locating a fluid leak in underground fluid conveying conduits typically require that a fixed delay be introduced into one of the sound data streams, thereby increasing the total analysis time, which is highly undesirable.
As another example, prior art methods and apparati for detecting and locating a fluid leak in underground fluid conveying conduits typically fail to compensate for variances in the ambient temperature, thereby compromising the accuracy of the calculation of the location of the source of leaks in the pipeline, which is highly undesirable.
As another example, prior art methods and apparati for detecting and locating a fluid leak in underground conduits typically analyze one set of sound data, which can be unreliable. Specifically, temporary noise can be created in the pipeline during moments of increased fluid usa
Kriegsman & Kriegsman
Radcom Technologies LTD
Wiggin David J.
Williams Hezron
LandOfFree
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