Underground conduit defect localization

• US 5,531,099 A
• Filed: 11/09/1994
• Issued: 07/02/1996
• Est. Priority Date: 11/09/1994
• Status: Expired due to Term

• Current Assignee: American Telephone & Telegraph Company (AT&T, Inc.), Lucent Technologies, Inc. (Nokia Corporation)
• Original Assignee: AT&T Corporation (AT&T, Inc.)
• Inventors: Russo, Anthony P.
• Primary Examiner(s): Williams, Hezron E.
• Assistant Examiner(s): Politzer, Jay L.
• Application Number:
  US08/336,452
• Time in Patent Office: 601 Days
• Field of Search: 73/592, 73/40.5 A
• US Class Current: 73/40.50A
• CPC Class Codes: G01M 3/243 for pipes

Abstract

A method of locating a defect in a buried conduit by sensing vibrations generated at the defect, processing signals detected by sensors to generate a cross-correlation function, smoothing this function to obtain a peak, calculating a center velocity of acoustic energy propagation, and using the center velocity of acoustic energy propagation to calculate the location of the defect.

Claims

1. A method of locating a leak in a conduit, comprising the steps of:

computing a cross-correlation function from leak noise data from said conduit obtained from a first pair of sensors including a first and second sensor coupled to said conduit at a spaced interval for obtaining a raw plot of a first time differential for said leak noise to traverse said spaced interval;

computing a cross-correlation function from leak noise data obtained from a second pair of sensors including said second sensor and a third sensor coupled to said conduit at a second spaced interval for obtaining a raw plot of a second time differential for said leak noise to traverse said second spaced interval;

smoothing each raw plot of time differential by computing an envelope having a single peak for obtaining a peak time differential in each plot;

determining the velocity of propagation for leak noise in the conduit using the first peak time differential and the known spacing between the first pair of sensors; and

determining the location of the leak using the velocity of propagation, the second peak time differential, and the known spacing between the second pair of sensors.

2. The method of claim 1 further comprising synchronizing the recording of the leak noise data from each sensor along the conduit by providing a synchronization pulse.

3. The method of claim 2 further comprising synchronizing the recording with a radio signal.

4. The method of claim 1 further including analog to digital conversion means and comprising converting the leak noise data from three spaced apart locations along the conduit from analog to digital form.

5. The method of claim 1 further comprising filtering leak noise data to pass a particular frequency band.

6. The method of claim 1 further comprising filtering the leak noise data to exclude single frequency tones.

7. The method of claim 1 further comprising correcting the location calculation by including the rate and direction of flow of a medium within the conduit for determining the final leak location.

23. The method claim 5, wherein said frequency band includes frequencies in a range between 4000 and 8500 Hz.

24. The method of claim 6, wherein said single frequency tones are removed by means of a Smoothed Coherence Transform (SCOT).

25. The method of claim 1, wherein said spaced interval between said first and second sensor is between 1 and 10 feet.

26. The method of claim 7, wherein said rate and direction of flow are calculated utilizing the following steps:

imposing a first vibration upon the conduit at a position proximate a first sensor in a pair of sensors, said position being outside of a region located between said pair of sensors which are separated by a distance and mounted to the conduit;

detecting a first transmitted vibration propagating along the conduit in response to said imposed vibration at both sensors;

repeating the steps above wherein a second vibration is imposed at a second position proximate a second sensor in said pair of sensors, said position being outside of said region located between said pair of sensors;

determining the center velocity of each transmitted vibration by computing an envelope correlation function; and

calculating the direction of fluid flow and its velocity.

8. A method of locating a leak in a conduit, comprising the steps of:

providing sensors for sensing leak noise propagating in the conduit at three spaced apart locations along its length for generating an electrical signal at each location;

recording each signal in digital form;

computing a cross-correlation function from leak noise data obtained from a first pair of sensors including a first and second sensor coupled to said conduit for obtaining a raw plot of a first time differential for said leak noise to traverse an interval between said first and second sensor;

computing a cross-correlation function from leak noise data obtained from a second pair of sensors including said second sensor and a third sensor coupled to said conduit for obtaining a raw plot of a second time differential for said leak noise to traverse an interval between said second sensor and third sensor;

smoothing each raw plot of time differential for obtaining a peak time differential in each plot;

determining the velocity of propagation for leak noise in the conduit using the first peak time differential and the known spacing between the first pair of sensors;

determining an uncorrected location of the leak using the velocity of propagation, the second peak time differential, and the known spacing between the second pair of sensors; and

adjusting the uncorrected location calculation by including the rate and direction of flow of a medium within the conduit for determining the final leak location.

9. The method of claim 8 further comprising synchronizing the recording of the leak noise data from each sensor along the conduit by providing a synchronization pulse from a receiver.

10. The method of claim 9 further comprising synchronizing the recording with a radio signal.

11. The method of claim 9 further including analog to digital conversion means and comprising converting the leak noise data from three spaced apart locations along the conduit from analog to digital form.

12. The method of claim 8 further comprising filtering leak noise data to pass a particular frequency band.

13. The method of claim 8 further comprising filtering the leak noise data to exclude single frequency tones.

14. The method of claim 8 wherein piezoelectric sensors are attached to the conduit at three spaced apart locations.

15. An acoustic method of locating a leak in a buried steam conduit having a fluid with multiple velocities of acoustic energy contained therein, comprising the steps of:

attaching sensors to the conduit at a first, second, and third location, respectively, where each location is separated by a known distance from the others;

sensing steam leak noise propagating in the conduit from waves propagating normal to an outside surface of said conduit with said sensors to thereby generate an electrical signal at each location proportional to said steam leak noise;

providing synchronization to a recording operation for signal processing;

recording each signal in digital form for preserving it;

filtering each signal to pass a frequency band from 4000 to 8500 Hz for discriminating against turbulent flow noise in the steam, noise transmitted by the conduit;

filtering each signal to exclude single frequency tones;

computing a cross-correlation function from leak noise data obtained from a first pair of sensors located along the conduit for obtaining a raw plot of a first time differential;

computing a cross-correlation function from leak noise data obtained from a second pair of sensors located along the conduit for obtaining a raw plot of a second time differential;

smoothing each raw plot of time differential for obtaining a peak time differential in each plot;

determining the velocity of propagation for leak noise in the conduit using the first peak time differential and the known spacing between the first pair of sensors;

determining an uncorrected location of the leak using the velocity of propagation, the second peak time differential, and the known spacing between the second pair of sensors; and

adjusting the uncorrected location calculation by including the rate and direction of flow of a medium within the conduit for determining the final leak location.

16. A method of determining the flow rate and direction of a medium within a conduit comprising the steps of:

coupling a pair of sensors to said conduit at a first and second location thereof;

imposing a first vibration upon the conduit at a position proximate a first sensor in said pair of sensors said position being outside of a region located between said pair of sensors which are separated by a distance and mounted to the conduit;

detecting a first transmitted vibration propagating along the conduit in response to said imposed vibration at both sensors;

repeating the steps above wherein a second vibration is imposed at a second position proximate a second sensor in said pair of sensors, said position being outside of said region located between said pair of sensors;

determining the center velocity of each transmitted vibration by computing an envelope correlation function; and

calculating the direction of fluid flow and its velocity.

17. The method of claim 16 wherein the vibrations are detected by piezoelectric crystals thereby being converted to electrical signals.

18. The method of claim 16 wherein the vibrations are imposed by a transducer.

19. The method of claim 16 wherein vibration data is converted from analog to digital form.

20. The method of claim 16 further comprising filtering vibration data to pass a particular frequency band.

21. The method of claim 16 further comprising filtering the vibration data to exclude single frequency tones.

27. The method of claim 16, wherein said flow rate is calculated as half of the difference between the center velocities and said direction corresponds to the greater one of said velocities.

22. An acoustic method of determining the flow rate and direction of steam flowing in a conduit, comprising the steps of:

attaching a sensor to the conduit at a first and second location along the conduit, where each location is separated by a known distance from the other;

imposing a first vibration upon the conduit at a position proximate a first sensor in said pair of sensors, said position being outside of a region located between said sensors;

detecting a first transmitted vibration propagating along the conduit in response to said imposed vibration at both sensors;

imposing a second vibration upon the conduit at a second position proximate a second sensor in said pair of sensors, said position being outside of said region located between said pair of sensors;

detecting a second transmitted vibration propagating along the conduit in response to said imposed vibration at both sensors;

converting signals produced from said sensors from analog to digital form;

recording each signal in digital form for preserving it;

filtering each signal to pass a frequency band from 4000 to 8500 Hz for discriminating against turbulent flow noise in the steam, noise transmitted by the conduit;

filtering each signal to exclude single frequency tones;

computing a cross-correlation function from data obtained from the sensors from the first imposed vibration propagating along the conduit for obtaining a raw plot of a first time differential;

computing a cross-correlation function from data obtained from the sensors from the second imposed vibration propagating located along the conduit for obtaining a raw plot of a second time differential;

smoothing each raw plot of time differential for obtaining a peak time differential in each plot;

determining the first center velocity of propagation of imposed vibration in the conduit using the first peak time differential and the known spacing between the sensors;

determining the second center velocity of propagation of imposed vibration in the conduit using the second peak time differential and the known spacing between the sensors; and

calculating the flow rate and direction of the medium in the conduit, wherein said flow rate is calculated as half of the difference between said first and second center velocity and said direction corresponds to the greater one of said first and second velocity.