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METI~OD AND DEVICE FOR DETECTING
AND LOCATING LEAKS IN PIPELINES
TECHNICAL FIELD
This invention relates to a device and method for detecting and locating leaks in pipe. More particularly, this invention relates to a leak locator probe for insertion into a pipe for detecting leaks therein and related apparatus.
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1 159~24 ~' BACKGROUND ART
A method and device for detecting and locating leaks in buried pipelines is disclosed in U.S. Patent No.
3,817,086 to Dorgebray. That reference discloses a method 5 and device for detecting and locating leaks in buried pipes that includes a detection scraper piston that is moved with a flow of liquid being transported in the pipeline.
The detection scraper piston is driven by the liquid flow in the pipe and utilizes a differential pressure measuring 10 device that includes pressure-sensing elements. The pressure-sensing element can be a strain gauge carried by a deformable diaphragm or other pressure transducers having low inertia. The method of leak detection consists in continuously measuring the displacement of the piston 15 from a predetermined zero point as well as the difference between the pressure within the compartment and an intermediate pressure between those prevailing on the upstream and downstream sides of the piston.
There are other methods for detecting leaks in oil 20 pipelines. Some of these methods entail the use of radioactive tracers and consist of passinc3 through the pipeline a volume of fluid in which a radioactive tracer has been dispersed, usually bty dissolution, then removing practically the entire tracer content from the pipe by t 25 rinsing, and if necessary, by passing the scraper piston within the interior and finally in moving a detector piston through the line in order to detect the points at which the tracer has sorbed in the soil surrounding the pipeline after escaping from the pipeline through leaks 30 during passage of the radioactive fluid. For example, a method of this type is described in French Patent No.
2~088,609. r ~ t 5992~ j ,~
DISCLOSURE OF THE INVENTION
In accordance with the present invention, a method and device for detecting and locating leaks in pipelines is provided. The apparatus includes a detection probe 5 including a sensor, and electrical circuitry is provided to monitor a change in airflow at the sensor that is located within the probe. The probe is dimensioned and adapted for insertion into and through a pipe. In accordance with one embodiment of the present invention, 10 the apparatus includes a tube having a first open end and a second open end, with an aperture being located in the wall of the tube. An airflow measuring device is utilized as an airflow sensor in the probe and is disposed adjacent the aperture. In one embodiment the airflow measuring A
15 device is a temperature-stabilized heater. The heater maintains itself at a constant, elevated (above ambient) temperature. A separate, annular sealing ring is located adjacent each end of the tube for defining an annular volume within the pipe adjacent the tube, the annular 20 volume being bounded by the pipe, the tube and the sealing rings.
The electrical circuitry provided includes a voltage source for driving the temperature-stabilized heater, a first differential amplifier for amplifying the signal 25 from the heater and voltage divi~er for zeroing the first differential amplifier. The output of the first differential amplifier inputs into a milliamp meter for monitoring the current drawn by the temperature-stabilized heater. When an airflow at ambient temperature, such as 30 the air temperature in a sewer pipe, impinges the heater, it draws additional current to maintain itself at a constant elevated tempe-rature. By correlating the amount of current drawn by the heater with the airflow, the airflow can be determined by monitoring the current 35 supplied to the heater. In accordance with one embodiment of the circuitry, the output of the first amplifier goes into the input of a second amplifier that is utilized as ~ , . .. . ..
1 1 5992~
a comparator saturating amplifier, such that when its output rises above a certain threshold level, it will activate a transistor which causes electrical current to be supplied to an audio buzzer. The threshold value is calibrated such that it corresponds to a particular volumetric flow rate through the aperture.
In accordance with another aspect of the present invention, a method for detecting leaks in pipes is provided comprising pressurizing the volume defined by the interior of the pipe to be tested to a pressure in excess of the air pressure surrounding the pipe and then moving through the pipe a leak locator probe in accordance with the invention. Airflow detected through the aperture by the airflow measuring device is monitored, thereby indicating the presence of a leak.
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BRI EF DE:SCRI PTION OF THE DRAWI~IGS
The invention can be more completely understood by reference to the accompanying drawings in which: ' FIGURE 1 is a side elevational view of a leak S locator probe in accordance with the present invention in position within a pipe to be tested;
FIGURE 2 is an elevational view of one end of a leak locator probe in accordance with the present invention;
FIGURE 3 is a sectional elevational view along lines 3-3 of FIGURE 2; and FIGURE 4 is a schematic diagram of the electrical circuitry utilized to measure fluid flow through a leak locator probe in accordance with the present invention.
~ 159924 DETAILED ~ESCRI PTION
In accordance with the present invention, an apparatus and method for detecting fluid leaks in a r pipe is provided.
Referring to FIGURES 1-3, there is depicted a leak locator probe 10 in accordance with the present invention shown in position inside a pipe 12 for detecting leaks in pipe 12. Leak locator probe 10 preferably includes a provision for attachment of a cable to either end thereof as hereinafter described, to facilitate movement of leak locator probe 10 through a pipeline.
As shown in FIGURE 1, leak locator probe 10 can be moved along the length of pipe 12 in either direction by applying a force through a cable 14 or 16, which are E
attached to opposite ends of leak locator probe 10.
Leak locator probe 10 is constructed of a tube 17 that is preferably relatively thin-walled. Tube 17 may be constructed from any suitable material and may be metallic or plastic. Leak locator probe 10 further includes sealing rings 1~. A separate sealing ring 18 is disposed at each end of tube 17 for defining an annular volume 19 ~ithin pipe 12 adjacent leak locator probe 10. Annular volume 19 is bounded by pipe 12, tube 17 and sealing rings 18.
Preferably, the annular sealing rin~s are constructed of rubber and in the most preferred embodiment the annular sealing rings are constructed of a three-ply cloth inserted synthetic butyl rubber marketed by the Buckeye Rubber Company of Lima, Ohio. The annular sealin~ rings are dimensioned to provide a seal between the leak locator probe and the pipe.
An aperture 20 is located in the wall of tube 17 for providing a fluid passageway between annular volume 19 and the interior portion of tube 17. An airflow sensing device 22, preferably a temperature-stahilized heater, is disposed adjacent aperture 20 and is utilized r t to measure volumetric airflow through aperture 20, as will be hereinafter déscribed in greatér detail. Any suitable method of mounting the sensing device can be utilized. Preferably a cover 23 is provided to protect 5 airflow sensin~ device 22 without preventing airflow through aperture 20. Any suitable attachment arrangement can be utilized, such as rivets 23a.
Tube 17 has mounted on each end thereof a separate sleeve 24, as shown in FIGURE 3 the exterior end portion 10 of each sleeve 24 is preferably threaded to allow sealing rings to be secured thereto as will hereinafter be described. Preferably, sleeves 24 are secured to tube 17 by a series of nut-and-bolt arrangements 26 as shown in FIGURE 3. An eye 28 forms part of each nut-and- g 15 bolt arrangements 26 and is located on the interior portion of tube 17 to facilitate securement of a cord or cable thereto for transportin~ leak locator probe 10 through a pipe. Preferably, four nut-and-bolt arrangements 26 are utilized at each end of leak locator 20 probe 10 to fasten adequa~ely thereto a sleeve 24 and to distribute forces evenly on leak locator probe ln that may be exerted through either of cables 14 or 16.
A short length of a cable 30, one for each nut-and-bolt arrangements 26, is secured to each eye 28 with the 25 other ends of cables 30 being secured together to form an attach~ent loop 31 at each end of leak locator probe 10, to which cables 14 and 16 are attached for moving leak locator probe 10 through a pipe. Further, cahle 14 may be used as a ground line for airflow sensor 22, when, 30 for example, sensor 22 require~s a current source to operate, such as a temperature stabilized heater. An electrical line 32 forms a connection between sensor 22 and cablé 14. Also, an electrical line 33 provides the other connection with a volta~e source.
Sealing rings 18 are utilized to provide a seal between the pipe wall and leak locator probe 10.
Preferably, a pair of stiffening discs 34 are utilized ~_ . ...
to ~rovide support for each of sealing rings 18 for controlling the degree that sealing rin~s 18 can flex or bend when probe 10 is pulled throu~h a pipe. Sealing rings 18 and stiffening discs 34 are dimensioned such that the interior diameter thereof is slightly greater than the outer diameter of sleeves 24 along the threaded portion with the interior diameter of sealing rings 18 and stiffening discs 34 being less than the outer diameter of the non-threaded portions of sleeves 24 thereby allowing the sealiny rings and stiffening discs to be fixedly secured between a shoulder portion 35 of sleeves 24 located at the point where the threaded portion of sleeves 24 terminates and an end ring 36. ~nd ring 36 has on its interior portion threads that correspond with the threads of sleeves 24 to allow end rin~s 36 to be secured against stiffening discs 34 with a sealing rin~ 18 located between each pair of stiffening discs 34.
In accordance with the preferred embodi~ent of the present invention, leak locator probe 10 includes airflow sensor 22 that is a temperature-stabilized heater, referred to in FIGURE 4 by reference numeral 38, disposed adjacent aperture 20 for measuring volumetric airflow through aperture 20. Referrin~ to FIGURE 4, there is depicted a schematic diagram of the electrical circuitry used in conjunction with temperature-stabilized heater 38 for measuring fluid flow through aperture 20 in detecting leaks within a pipe. The circuitry is designed for use with a direct current source 39, such as an automobile battery, for example. A low voltage cutoff is provided between heater 38 and current source 39. A rotary power switch 40 is mounted on a common shaft with a rotary switch 4~ that is calibrated in threshold activation values that correspond to a rate of airflow through aperture 20 for activating an alarm. Diodes 44 and 46, resistors 48 and 50, transistor 52, induction coil 54 and relay 56 are connected as shown in FIGURE 4 to provide a controlled voltage supply for heater 38. Heater 38 is ~ ~ ' constructed such that it maintains itself at a constant elevated temperature by drawing current. In a steady-state condition (no airflow through aperture 20) heater 38 draws a constant amount of current. When air impinges heater 38, it will require more current to maintain itself at its reference temperature thereby causing a large voltage drop across a resistor 58. There is also a small change in the voltage drop across heater 38. This voltage drop is sensed by resistors 60 and 62 that are connected in parallel with heater 38. When the voltage drop across resistor 58 is large enough, transistor 64 is activated thereby energizing light emitting diode 66. Light emitting diode 66 is mounted on a control panel (not shown) and its activation indicates that heater 38 is drawing a maximum current indicating a very large airflow through aperture 20. A differential amplifier 67 obtains an input between resistors 60 and 62.
A resistor 68 is mounted in series with the input to differential amplifier 67 and a tie-on point between resistors 60 and 62. Resistors 60, 61 and 62 are biasing resistors for transistor 64.
Resistors 70 and 72 and variable resistor 74 are utilized as a voltage divider network for the other input to differential amplifier 67. This voltage divider network is utilized to zero the input to differential amplifier 67. The output ~f differential amplifier 67 is fed to a milliamp meter 76 which is also preferably located on a control panel. Resistors 78, 80 and 82 are utilized to bring that side of milliamp meter 76 to a voltage slightly above ground. A resistor 84 is connected between the inputs to differential amplifiers 67 and 86.
The output of amplifier 67 goes into the input of differential amplifier 86 which is utilized as a comparator saturating amplifier such that when its output, directed through resistor 88, exceeds a certain threshold value level, it will activate transistor 90 thereby providing a power source to buzzer 92. The activation of r buzzer 92 transmits an audio signal. Buzzer 92 may be mounted directly on leak locator probe 10 or buzzer 92 may be mounted at a remote location. The voltage to transistor 90 can be adjusted by means of a rotary switch 94 from which one of five resistors, 96, 98, 100, 102 and 104 may be selected, thereby changing the airflow rate through aperture 20 that is required to activate buzzer 92. Each resistor 96, 98, 100, 102 and 104 is calibrated to correspond to an output from differential amplifier 86 that corresponds with a particular airflow rate through aperture 20. A resistor 106 is also connected in series between rotary switch 94 and rotary switch 39. As stated previously, rotary switch 94 and rotary switch 42 have a common shaft so that setting one switch auto~atically sets the other.
In accordance with the preferred embodiment of the invention, the heater utilized is sold by the National Semiconductor Company, Part No. LM399. LM399 is a precision, temperature-stabilized monolithic zener and heater that requires a relatively low power for stabilization at a constant temperature. Only the heater portion of the circuitry is utilized. Generally this device is sold with insulating material that encloses the device. As utilized in accordance with the present invention, this insulation is removed from the device prior to use in the leak locator probe to reduce any lag time that would be caused by the insulation when, for example, air impinges the device. Preferably, transistor 64 is Motorola Part No. 2N3906, transistor 52 30 is Motorola Part No. 2N3904, transistor 90 is Motorola Part NoO 2N3904 and amplifiers 67 and 86 are preferably on a single chip, National Semiconductor Part No. LM358, with the pin positions 1-8 being identified in FIGURE
4 as reference numerals lA-8A, respectively.
In accordance with the method of the present invention, leaks are located in pipes, such as sewer lines, for example. In accordance with this method, the r ~
ends of the length of pipe to be tested are plugged, preferably utilizing test plugs sold under the trademark "SPI" by the AGL Corporation of Jacksonville, Arkansas.
The test plugs should provide an airtight seal between the plug and the pipe and also have provisions for allowing a cable to pass through the plug for pulling the leak locator probe through the pipe. After the ends of the pipe have been plugged, the pipe is pressurized with a gas to a pressure greater than the pressure at the exterior of the pipe. Leak locator probe 10 is then transported along the length of the pipe while monitoring the current drawn by airflow sensor 22 that is mounted adjacent aperture 20. When leak locator probe 10 is adjacent a leak in pipe 12, such that the leak communicates with annular volume 19, an airflow will occur through the leak from the region of high pressure to the region of lower pressure thereby causing an airflow to occur through aperture 20. This results in airflow sensing device 22 detecting airflow through aperture 20, indicating th~ presence of a leak.
In accordance with the invention, other systems rnay be utilized for transmitting a signal that is proportional to the airflow to a monitoring location at a point located-exteriorly of the pipe. For example, the audio signal provided by buzzer 92 can be transmitted through the length of pipè being tested, the pipe acting as a waveguide for the audio signal. A microphone can be located at one end of the pipe for receiving the audio signal. Further, the towing cable for moving the leak locator probe through a pipe can incorporate a fiber optics system for transmitting the signal that is proportional to the airflow. In addition, a magnetic telemetry system can also be used for transmitting a signal from the airflow measuring device when the probe is in a pipe to a monitoring location located exteriorly of the pipe. Such a system could also be utilized to pinpoint the exact location of the leak locator probe 1 15992,~
with respect to the pipe. A radio signal could also be similarly used. The cable could be utilized to transmit the magnetic or radio signal. In another embodiment, the signal could be transmitted directly through the earth eliminating the need for a cable to transmit the signal. This would be especially useful if the leak locator probe had a self-contained propulsion system for moving it along the length of pipe. Optical coupling could be utilized using infra red diodes, laser diodes or visible light with a photocell sensor located at one end of the pipe for receiving a signal from the probe.
While this invention has been described with respect to its preferred embodiments, it is apparent that numerous changes, modifications and rearrangements are possible and are intended to be within the scope of the appended claims.
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