Abstract:
The pipeline leak detector is a mobile device having a pressure sensor array for travel within a fluid pipeline for leak detection in the pipe wall. The sensor array is positioned close to the internal surface of the pipe wall and rotates circumferentially about the surface of the pipe wall as the device travels through the pipe, thus describing a helical path along the pipe wall to cover the entire internal surface of the pipe wall with a minimal number of sensors. The sensors comprise tubes with conical mouths, and flexible members and strain gauges within the tubes. Pressure changes due to leaks cause the flexible members to move, with the strain gauges sending signals to a central processor to indicate a leak. The device is supported by a drive wheel, a driven wheel, and an idler wheel bearing against the internal surface of the pipe and evenly circumferentially spaced.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation-in-part of our prior U.S. patent application Ser. No. 13/899,527, filed May 21, 2013. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to fluid conveyance using pipes, conduits, and the like, and particularly to a pipeline leak detector employing a drive system for the helical motion of an array of pressure sensing ports along the interior wall of the pipe. 
     2. Description of the Related Art 
     Oil and natural gas are likely the two fluids that are first considered when the transport of fluids through pipelines is considered. However, water is a very valuable commodity in many arid parts of the world and water transport via pipelines is a major industry in many areas. Accordingly, considerable research and development has gone into the development of technologies directed to the detection of water leaks in water pipelines. Various principles of leak detection have been developed, including acoustic leak noise correlators and surface listening devices, ground penetrating radar, infrared thermography, and chemical tracing. These methods or principles have a number of limitations when used for the detection of leaks in water distribution networks or pipe systems. The apparatus for these leak detection systems and devices can be quite costly, and their use may be labor intensive and time consuming. Moreover, the results may not be sufficiently accurate and may have noise interference problems in the case of acoustic leak detection systems. All depend at least to some extent upon the material of which the pipe is formed. 
     Acoustic (noise) detectors are widely used by various municipalities to detect leaks in water lines. Acoustic systems work well in metal pipe, but the effectiveness of acoustic leak detection is questionable with plastic pipe due to high signal attenuation, low frequency content, and the fittings and joints along the pipes affecting acoustic wave propagation. A relatively recent development has been the use of “pigs,” or robotic devices that travel through the interior of the pipeline using pressure differential sensors to detect leaks. These in-pipe mobile sensors, e.g., Sahara® and Smartball®, may overcome many of the shortcomings of conventional acoustic leak detection systems. The desirability of such in-pipe mobile sensors arises from their ability to survey relatively long distances through pipelines in a pipe network, which may be difficult to access using other leak detection techniques. 
     One limitation of such pressure differential sensors in in-pipe mobile systems is the necessity of placement of the sensors extremely close to the leak, due to the relatively small pressure gradient until very close to the leak. When a sufficient number of detectors is provided, leak detection is less dependent upon pipe material (metal or plastic), pipe depth and soil type, background noise, and perhaps other factors. However, a small leak in a pipe wall may subtend only a small fraction of the internal circumference of the pipe. Accordingly, a large number of pressure sensors are conventionally required in order to cover substantially the entire internal circumference of the pipe as the mobile apparatus travels through the pipe. As an example, a pipe having a diameter of 30 centimeters (cm) would have an internal circumference on the order of 100 cm. A 2 millimeter (mm) diameter leak would require about 50 detectors arranged in a circumferential array about an in-pipe traveling leak detector device for such a pipe, if each of the detectors could cover a lateral span of 1 cm along the pipe wall. 
     Thus, a pipeline leak detector solving the aforementioned problems is desired. 
     SUMMARY OF THE INVENTION 
     The pipeline leak detector is a mobile device, i.e., a pipeline “pig,” adapted for travel within and through a fluid pipeline for the detection of leaks within the pipeline. The device includes a single pressure sensor array disposed adjacent to the internal surface of the pipe wall. The sensor array is formed of three or four closely spaced, generally funnel-shaped leak detectors having flexible valves or diaphragms therein. Strain gauges or sensors are attached thereto to provide a signal when the valves or diaphragms are moved due to changes in pressure from an adjacent leak. The sensor array thus subtends only a fraction of the internal circumference of the pipe. A mechanism is provided to rotate the sensor array about the internal circumference of the pipe as the leak detector travels longitudinally through the pipe. Thus, the sensor array describes a helical path along the interior surface of the pipe wall to insure complete coverage of the entire internal surface of the pipe. Spacing between the pressure sensor array and the interior surface of the pipe wall is carefully controlled for optimum results. 
     The leak detector includes a drive and support portion having three wheels extending radially therefrom, evenly separated by 120° of arc. All three wheels bear against the internal surface of the pipe wall, and serve to center the leak detector within the pipe. One of the wheels is a powered drive wheel that provides propulsion to drive the detector through the pipe. Another of the wheels is rotated by its frictional engagement with the interior surface of the pipe wall. This wheel communicates rotationally with the pressure sensor array in order to rotate the array circumferentially about the interior of the pipe wall to describe the helical path as the leak detector travels through the pipe. The third wheel is an idler or stabilizer wheel and rolls passively along the internal surface of the pipe wall to provide a third point of contact of the leak detector with the pipe wall. The axial alignment of the rotational paths of the three wheels precludes any axial rotation of the drive and support portion of the apparatus within the pipe. 
     Electronic componentry may be included with the leak detector. The stabilizer wheel (or one of the other wheels) may serve as an odometer, transmitting distance traveled to a central processor. The pressure sensors signal the processor when a drop in pressure is detected along the pipe wall, also providing their circumferential position about the pipe wall when the leak is detected. This information as to the axial location of the leak detector in the pipe and the circumferential position of the affected sensor array may be stored in the central processor, or may be transmitted to a data retrieval source external to the pipe, if such equipment is provided. 
     These and other features of the present invention will become readily apparent upon further review of the following specification and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an environmental elevation view in section of a pipeline showing the pipeline leak detector according to the present invention disposed therein, illustrating various details thereof. 
         FIG. 2  is a section view along lines  2 - 2  of  FIG. 1 . 
         FIG. 3  is an elevation view of the sensor holding wheel and leak sensors disposed thereon of the pipeline leak detector of  FIG. 1 . 
         FIG. 4  is an elevation view in section of a first embodiment of a leak sensor of the pipeline leak detector of  FIG. 1 . 
         FIG. 5  is an elevation view in section of a second embodiment of a leak sensor of the pipeline leak detector of  FIG. 1 . 
         FIG. 6  is a schematic section view through a pipeline illustrating the helical path traveled by the sensors of the pipeline leak detector according to the present invention. 
         FIG. 7  is an elevation view in section of a portion of a pipeline having a leak therein, illustrating the pressure pattern disposed about the leak. 
     
    
    
     Similar reference characters denote corresponding features consistently throughout the attached drawings. 
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The pipeline leak detector is a “pig” type device adapted for robotic travel within a fluid pipeline for the detection of fluid leaks in the pipeline wall. The device accomplishes this with a minimal number of sensors. The sensors rotate within the pipe to cover the entire interior surface of the pipe wall as the device travels through the pipe. The pipeline leak detector is particularly well suited for use in water pipelines, but may be adapted for use in pipes carrying oil, gas, and/or other fluids as well. 
       FIG. 1  of the drawings provides an elevation view in section of the pipeline leak detector  10  disposed within a pipe P. The leak detector  10  has a rotationally stationary drive component  12  having a central housing  14 . The drive component and its housing are restrained from axial rotation within the pipe P by a series of supporting wheels, described in detail further below. A rotary driveshaft  16  extends axially from the drive component  12  and its housing  14 . The driveshaft  16  has a drive component end  18  disposed within the housing  14  and an opposite sensor array end  20 . A leak detector component  22  is disposed upon the sensor array end  20  of the driveshaft  16 . The leak detector component  22  has a single leak sensor array  24  extending radially therefrom that subtends a limited arc (e.g., thirty degrees, more or less) about the leak detector component  22 . 
     The sensor array  24  comprises a plurality of pressure sensors  26  extending radially from a sensor array support wheel  46 , which is installed concentrically about the central body of the leak detector component  22 . The sensors  26  are adapted for the detection of minor pressure changes along the wall of the pipe P as the device  10  travels through the pipe. The leak detector component  22  and the sensor array  24  extending radially therefrom are driven in axial rotation within the pipe P as the rotary driveshaft  16  rotates. The leak sensors are force sensors, having either a gate or a membrane that moves and generates an electronic signal when a leak is detected. Two different pressure sensor embodiments are described herein, which are illustrated in  FIGS. 4 and 5 , respectively, and described in detail further below.  FIGS. 2 and 3  also illustrate sensor arrays  24 . The array of  FIG. 2  has four sensors  26 , and the array of  FIG. 3  shows three such sensors  26 . The precise number of sensors is adjusted in consideration of the diameter of the pipe P, the diameters of the sensors  26 , and the axial and radial velocities of the sensors as they travel through the pipe P. 
     The drive component  12  and central housing  14  of the leak detector  10  are supported by three radially disposed wheels. The wheels travel along the interior surface of the pipe wall as the device  10  travels through the pipe. The three wheels are distributed evenly about the circumference of the leak detector  10  and are separated by substantially equal angular arcs A of about 120° each, as shown in  FIG. 2  of the drawings. A rotationally powered drive wheel  28  rolls along the interior surface of the pipe P wall. The drive wheel  28  provides motive power for the leak detector  10  to drive the device  10  through the interior of the pipe P. The drive wheel  28  may be powered by a small electric motor disposed within the wheel hub. The motor receives electrical power from an on-board electrical storage battery disposed within the drive component  12 . Such motors and electrical power battery systems are well known, and accordingly are not described in further detail herein. 
     A driven wheel  30  extends radially from the central housing  14  and rolls along the interior of the pipe P. The driven wheel  30  has a concentric first bevel gear  32   a  at its hub. The first bevel gear  32   a  drives a second bevel gear  32   b  disposed upon the distal end portion  34   b  of a driven wheel shaft. The shaft has a proximal end portion  34   a  disposed within the central housing  12  and extending radially therefrom. The distal end portion  34   b  telescopes within the proximal end portion  34   a  to allow the driven wheel shaft assembly to lengthen and shorten according to the diameter of the pipe P. The two driven wheel shaft portions  34   a  and  34   b  are locked rotationally to one another by splines, key and keyway, non-circular sections, or other conventional means. A third bevel gear  36   a  is affixed to the proximal end portion  34   a  of the driven wheel shaft assembly. A fourth bevel gear  36   b  is affixed to the drive component end  18  of the leak detector component driveshaft  16  and meshes with the third bevel gear  36   a , as shown in  FIG. 1 . This gear train drives the leak detector component driveshaft  16  and the leak detector component  22  extending therefrom rotationally as the driven wheel  30  rotates due to its frictional engagement with the wall of the pipe P as the leak detector  10  travels through the pipe. Alternative means of transmitting the rotary motion of the driven wheel  30  to the driveshaft  16  may be provided, e.g., a flexible shaft, hydraulics, etc. 
     The third wheel is an idler or stabilizer wheel  38  extending radially from the drive component  12 , or more properly from its central housing  14 , and serves primarily as a third point defining the transverse span of the drive component  12  across the interior of the pipe P. The idler or stabilizer wheel  38  is a passive support wheel with no drive means, i.e., no means of propelling the leak detector  10  through the pipe P, and has no means of driving the rotation of the driveshaft  16  and its leak detector  12 . However, the stabilizer wheel  38  may include means for transmitting its rotary motion to a central processor (discussed further below) for translation to distance traveled by the pipeline leak detector  10  as it travels through the pipe P. This function may alternatively be handled by one of the other two wheels  28  or  30 , particularly the driven wheel  30 , as it is already imparting rotary motion to the driveshaft  16  that is connected to the drive component  18  of the device. 
     The driven wheel shaft can adjust inward and outward to adjust for different pipe diameters by means of its mutually telescoping proximal and distal portions  34   a  and  34   b , as noted above. Accordingly, the positions of the three wheels  28 ,  30 , and  38  may be adjusted for different pipe diameters. Each of the wheels is supported by an adjustable length strut that extends radially from the drive component  12 , or more properly, from the housing  14  of the drive component. The drive wheel  28  is supported by a drive wheel strut having a proximal portion  40   a  and a distal portion  40   b  that telescopes in and out of the proximal portion  40   a  to adjust its length. The driven wheel  30  is supported in the same manner by a driven wheel strut having a proximal portion  42   a  and a distal portion  42   b  that telescopes in and out of the proximal portion  42   a . The idler or stabilizer wheel  38  is also supported in the same manner by a stabilizer wheel strut having a proximal portion  44   a  and a distal portion  44   b  that telescopes in and out of its proximal portion  44   a . The pipeline leak detector  10  may thus be adjusted for use in different diameters of pipes P by adjusting the lengths of the driven wheel shaft, the three wheel struts, and the radial spans of the sensors  26  of the sensor array  24 . 
     The longitudinal or axial motion of the pipeline leak detector  10  through the pipe P results in a rotary motion of the leak detector component  22  and its sensor array  24  by means of the drive wheel  30  and its driveshaft and gearing, as described in detail further above. The drive component  12  of the leak detector is restricted from rotating about its longitudinal axis within the pipe P due to the alignment of the wheel rotation or tracks parallel to the longitudinal axis of the pipe. However, the combination of the longitudinal motion of the leak detector  10  and the rotary motion of the leak detector component  22  and its sensor array  24  results in the sensor array  24  describing a helical path H immediately adjacent the inner surface of the pipe wall, as shown in  FIG. 6  of the drawings. (The helical path illustrated in  FIG. 6  is shown in its complete appearance through 360° of rotation within the inner circumference of the pipe P.) The diameter of the drive wheel  30  and the gear ratios of the first through fourth bevel gears  32   a ,  32   b ,  36   a , and  36   b  are selected to provide complete coverage of the interior of the pipe wall as the sensor array  24  travels along its helical path H. It will be seen that by increasing the rotational speed of the leak detector component  22  relative to the longitudinal speed of the device  10  through the pipe P, it is possible to use only a single leak detector array  24 . 
     The pipeline leak detector  10  is adapted to travel through a pipeline P carrying water, oil, gas, or other fluid in search of leaks L, as shown in  FIG. 7  of the drawings. Any leak L will result in a pressure drop across the leak, as the fluid flows from the relatively higher pressure within the pipe P to the lower pressure outside the pipe (or vice versa) and the flow accelerates through the leak aperture.  FIG. 7  provides a representation of this phenomenon. The pressure is represented by a series of isobars I 1  through I 8  (with other closely spaced isobars being shown within the leak aperture). The more closely spaced the isobars are over a given distance or span, the greater the pressure drop over the given distance. The pressure drop within the pipe P, represented by the isobars I 1  through I 4 , is of primary interest here. It will be noted that in order to detect this pressure drop, the detector or sensor must be quite close to the leak L, as the pressure does not change significantly at some distance from the leak, as indicated by the relatively widely spaced isobars I 1  and I 2 . Accordingly, the helical path H traveled by the sensor array  24  assures that complete coverage of the interior of the pipe wall will occur as the pipeline leak detector  10  travels through the pipe P so that at least one of the pressure sensors  26  passes nearly directly over the leak to register the pressure drop. 
     Returning to  FIG. 1  of the drawings, it will be noted that each of the pressure sensors  26  is connected to a central processor  48  by a wiring harness  50 . The central processor  48  receives pressure drop signals from each of the pressure sensing elements  26  whenever such a pressure drop is sensed by an individual sensor or sensors. The central processor  48  also communicates electronically with the rotationally stationary drive component  12 , e.g., via slip rings or other conventional means. The central processor  48  registers both the location of the leak detector  10  within the pipe P by means of the odometer information provided by one of the three wheels  28 ,  30 , or  38 , and also registers the angular relationship between the leak detector component  22  and its sensor array  24  relative to the drive component  12 . Thus, whenever a leak is detected, the central processor  48  records this information to enable a technician or other person to determine not only the axial location of the leak along the length of the pipe P, but also the circumferential location of the leak about the pipe. This information may be recorded by the central processor  48 , and/or may be transmitted to a remote external receiver  52  by an on-board transmitter  54  communicating with the receiver  52 , if desired. 
       FIGS. 4 and 5  illustrate two different pressure differential leak sensors, or more precisely, two different detectors that may be installed within the pressure differential leak sensor  26 . The pressure differential leak sensor  26  essentially comprises a radially disposed tube  56  having a support wheel attachment end  58  and an opposite outer end  60 , with a frustoconical mouth  62  extending from the outer end  60 . In the embodiment of  FIG. 4 , a flexible valve  64  extends across the juncture of the mouth  62  and the outer end  60  of the tube  56 . The valve  64  includes a strain gauge  66  thereon. The strain gauge  66  is electrically connected to the central processor  48  by a wiring harness  50 , as shown in  FIG. 1  of the drawings. As the mouth  62  of the sensor  26  passes over a leak, the drop in pressure at the leak results in fluid flow through the tube  56 , thus flexing the valve  64  outward as shown in  FIG. 4  as the fluid flows therethrough and altering the electrical characteristics of the attached strain gauge  66  to send a signal to the processor  48 . 
     The pressure differential leak sensor  26  of  FIG. 5  has an identical outer structure, i.e., tube  56  with its inboard attachment end  58  and opposite outer end  60  and frustoconical mouth  62  extending from the outer end  60 . However, rather than having an opening valve within the juncture of the outer end  60  of the tube and the frustoconical mouth  62 , a closed or sealed flexible diaphragm  68  is applied across this juncture. A strain gauge  66 , which may be substantially identical to the strain gauge illustrated in the embodiment of  FIG. 4 , is installed upon the flexible diaphragm  68 . The strain gauge  66  may be installed either outward or inward on the diaphragm  68  or the valve  64  of the embodiment of  FIG. 4 , as desired. As the mouth  62  of the sensor  26  of  FIG. 5  passes over a leak, the drop in pressure at the leak results in a differential pressure between the interior of the tube  56  and the mouth  62  of the tube, thus distending the sealed diaphragm  68  outward as shown in  FIG. 5  and altering the electrical characteristics of the attached strain gauge  66  to send a signal to the processor  48 . 
     It is to be understood that the present invention is not limited to the embodiments described above, but encompasses any and all embodiments within the scope of the following claims.