Pipeline mapping and interrupter therefor

• US 6,617,855 B2
• Filed: 03/23/2001
• Issued: 09/09/2003
• Est. Priority Date: 03/24/2000
• Status: Active Grant

• Current Assignee: Radiodetection Limited
• Original Assignee: Radiodetection Limited
• Inventors: Flatt, David William, Worsely, Robert Ashworth, Petherick, Stephen John
• Primary Examiner(s): Barlow, John
• Assistant Examiner(s): Le, Toan M
• Application Number:
  US09/815,911
• Publication Number:
  US 20010047247A1
• Time in Patent Office: 900 Days
• Field of Search: 324/326, 324/425, 324/220, 324/72, 324/713, 324/263, 324/71.2, 324/559, 702/64, 702/34, 702/33
• US Class Current: 324/326
• CPC Class Codes: C23F 13/04 Controlling or regulating desired parameters
• CPC Class Codes: G01N 17/02 Electrochemical measuring systems for weathering, corrosion or corrosion-protection measurement

Abstract

Cathodic protection voltages are used to resist the damage to pipes or cables from electrolytic effects. However, localised fields can lead to stray currents and may result in corrosion and it is therefore desirable to detect and analyse those stray currents. Frequently there are several pipes in the area of interest and so it is necessary to distinguish between those pipes. Therefore the cathodic voltage on the pipes is modulated, with different pipes having different modulations. This modulation may be applied using an interrupter. Orthogonal modulations with non-unitary aspect ratios improve the discrimination between the pipes whilst maximising the energy content of the modulation pattern. The analysis is improved when the interrupters are synchronised with each other and so repeating on the same time-base. This synchronisation may be achieved using an external time signal such as GPS. An interrupter which can be used in this regard is also proposed, and may be powered from the cathodic voltage itself.

Claims

1. A method of identifying underground pipes or cables by detecting currents on one or more said underground pipes or cables comprising:

modulating a negative voltage applied to the or each of said pipes or cables to produce a modulated current on the or each of said pipes or cables;

detecting the magnetic field produced by said current or currents; and

identifying the pipe or cable on which said current or currents are present by detecting the modulation of said current or currents.

2. A method of detecting currents on one or more underground pipes or cables according to claim 1, in which said modulation is a square-wave modulation of non-unitary aspect ratio.

3. A method of detecting currents on one or more underground pipes or cables according to claim 1, wherein said modulation is applied using an interrupter for the or each of said pipes or cables.

4. A method according to claim 3, in which there are a plurality of underground pipes or cables and the interrupters connected to each pipe or cable are synchronised with each other.

5. A method of detecting currents on a plurality of underground pipes or cables according to claim 4, wherein said synchronisation is achieved by each of the interrupters receiving an external time or clock signal.

6. A method of detecting currents on a plurality of underground pipes or cables according to claim 5, wherein said external time or clock signal is a GPS signal.

7. A method of detecting currents on a plurality of underground pipes or cables according to claim 4, wherein the modulation applied to the voltage on each pipe or cable is orthogonal to each of the modulations applied to the other pipes or cables.

8. A method according to claim 4, wherein

a first one of said pipes or cables is isolated prior to the detecting of the magnetic field produced by said current or currents on said first pipe or cables;

the position of said first pipe or cable from the detected magnetic field is determined;

said isolating, detecting and determining are repeated for each of said plurality of pipes or cables except one;

the magnetic field produced by currents on all of said plurality of pipes or cables is detected; and

the location of the remaining one pipe or cable is determined by subtracting the magnetic field due to the other pipes or cables from the magnetic field detected from all of said plurality of pipes or cables.

9. A method according to claim 4, wherein

a first one of said pipes or cable is isolated prior to detecting magnetic field produced by said current or currents on said first pipe or cable;

the position of said first pipe or cable from the detected magnetic field is determined;

the magnetic field produced currents on two of said pipes or cables is detected; and

the location of the second pipe or cable is determined by subtracting the magnetic field due to the first pipe or cable from the magnetic field detected from said two of said plurality of pipes or cables.

10. A method according to claim 1, further comprising:

a) detecting the magnetic fields from current or currents flowing in said pipe or cable at more than two sensors, each of said sensors producing a signal as a result of the magnetic field detected;

b) determining, from said signals, an estimated direction of said pipe or cable from each sensor;

c) generating a model of a virtual magnetic field generated by a virtual pipe with a current flowing in it;

d) modifying said signals such that the modified signals correspond to those produced by the superposition of said magnetic fields detected and said virtual magnetic field generated by said virtual pipe;

e) determining he change in said estimated directions due to said modification;

f) repeating c), d) and e) with said model being different on each repetition, until said estimated directions intersect at a common point, said mode being different by variation in the location and/or current of said virtual pipe.

11. A method according to claim 3, wherein a power storage device is connected between the or each said pipe or cable and ground, and the power stored in said power storage device to power the corresponding interrupter.

12. A method according to claim 5 further comprising:

modulating said applied negative voltage differently on each of said pipes or cables;

detecting the magnetic field produced by currents on a first of said pipes or cables;

analysing the current or currents at a first modulation, being the modulation applied to said first pipe or cable;

determining the components of said current or currents that are due to the pipe or cable itself or to background effects;

analysing the currents at each of the modulations applied to the other underground pipes or cables; and

determining the components of said current or currents that are due to linking between said first pipe or cable and each of the other pipes or cables.

13. A method of analysing currents on one of a plurality of underground pipes or cables according to claim 12, which each modulation is a square-wave modulation of non-unitary aspect ratio.

14. A method of analysing currents on one of a plurality of underground pipes or cables according to claim 12, wherein each modulation is applied using an interrupter for each of said pipes or cables.

15. A method of analysing currents on one or a plurality of underground pipes or cables according to claim 14, wherein the modulation applied to the voltage on each pipe or cable is orthogonal to each of the modulations applied to the other pipes or cables.

16. Apparatus for identifying underground pipes or cables by detecting currents in one or more of said underground pipes or cables to which a modulated negative voltage is applied in order to produce one or more modulated currents on the or each of said pipes or cables, apparatus comprising:

detecting means for detecting the magnetic field produced by said current or currents; and

means for identifying the pipe or cable on which said current or currents is present by detecting the modulation of said current or currents.

17. Apparatus according to claim 16, wherein the means for detecting the magnetic field is arranged to detect a square wave modulation of non-unitary aspect ratio.

18. A system comprising the apparatus of claim 16 and an interrupter for applying said modulation to the or each of said pipes or cables.

24. Apparatus according to claim 16, further comprising:

a plurality of detecting means each arranged to produce a signal detected as a result of the magnetic field detected;

direction determining means for determining an estimated direction of said pipe or cable from each detecting means;

generation means for generating a model of a virtual magnetic field generated by a virtual pipe with current flowing in it;

signal modifying means for modifying the signals from the detecting means, the signal modifying means being arranged such that the modified signals correspond to those produced by a superposition of the said detected magnetic fields and a virtual magnetic field generated by said generation means;

wherein said direction determining means are arranged to determine the change in said estimated directions due to a modified signal produced by the signal modifying means; and

wherein the generation means signal modifying means and direction determining means are arranged to produce repeated estimated directions until the estimated directions intersect at a common point, each said estimate being different by variation of the location and/or current in said virtual pipe.

19. A system according to claim comprising a plurality of interrupters, each interrupter arranged to modulate a different pipe or cable, and the interrupters are each arranged to be synchronised with each other.

20. A system according to claim 19, wherein the interrupters are arranged to be synchronised by each interrupter receiving an external time or clock signal.

21. A system according to claim 19, further comprising GPS receiving means for receiving an external time or clock signal as a GPS signal.

22. A system according to claim 19, wherein each interrupter is arranged to apply modulations which are orthogonal to the modulations each of the other interrupters is arranged to apply.

23. A system according to claim 19, further comprising position detecting means for detecting the position of one or more isolated pipes or cables by detecting the magnetic field produced and by said isolated pipes or cables;

and

means for determining the position of a further pipe or cable, said means for determining the position of a further pipe or cable being arranged to determine the total magnetic field produced by the or each said isolated pipe or cable and determine the position of the further pipe or cable by subtracting the total magnetic field produced by the or each said pipe or cable from the magnetic field detected by the detecting means.

25. A system according to claim 19, further comprising one or more power storage devices, each device arranged to be connected between one of said pipes or cables and ground, said power storage devices being arranged to power a corresponding interrupter.

26. A system according to claim 19, wherein each said interrupter is arranged to modulate each of said pipes or cables with a different modulation the system further comprising:

detecting means for detecting the magnetic field produced by currents on one or more of said pipes or cables;

analysing means for analysing the currents at different modulations;

linkage determining mean for determining the components of said currents that are due to linking between a first of said pipes or cables and each of the other of said pipes or cables.

27. A system according to claim 26, wherein each of said interrupters is arranged to produce a square-wave modulation of non-unitary aspect ratio.

28. A system according to claim 27, wherein each of said interrupters is arranged to produce a modulation which is orthogonal to the modulations each of the other interrupters are arranged to produce.

29. An apparatus for identifying underground pipes or cables by detecting currents in one or more of said underground pipes or cables to which a modulated negative voltage is applied in order to produce one or more modulated currents on the or each of said pipes or cables, apparatus comprising:

a detector to detect the magnetic field produced by said current or currents; and

means for identifying the pipe or cable on which said current or currents is present by detecting modulation of said current or currents.