Electromagnetic analysis of concrete tensioning wires

• US 20030164698A1
• Filed: 01/07/2003
• Published: 09/04/2003
• Est. Priority Date: 01/29/2001
• Status: Active Grant

• Current Assignee: Pure Technologies Limited (Xylem, Inc.)
• Original Assignee: Pure Technologies Limited (Xylem, Inc.)
• Inventors: Paulson, Peter O, McIntyre, John, Mitchell, Kevin
• Granted Patent: US 6,791,318 B2
• Time in Patent Office: Days
• US Class Current: 324/220
• CPC Class Codes: G01N 27/82 for investigating the presence of flaws
• CPC Class Codes: G01N 27/902 by moving the sensors
• CPC Class Codes: G01N 33/383 Concrete, cement

Abstract

Discloses methods to perform magnetic testing of tensioning elements in a pre-stressed concrete cylindcr, such as a pipe or water reservoir and testing apparatus. The apparatus includes magnetic flux production means and detector means disposed proximal to a surface of the cylinder in a plane in common with the magnetic flux production means that is orthogonal to an axis of the cylinder. The apparatus operates over a range of low frequency signals, for example, between 20 and 300 hertz or a pulse. Output of the inspection apparatus includes a signal and distance plot showing the results of testing a cylinder at one or more frequencies. In accordance with another method of analysis, a characteristic of the phase of the output over distance is plotted, including the phase or representations of the in-phase or quadrature components of the received signal in relation to the driving signal.

Claims

1. An inspection apparatus for detecting discontinuities in tensioning wires of a concrete pipe, comprising:

(i) driver means to induce a current in a metallic pre-stressing reinforcement of a concrete pipe;

(ii) detector means to produce an output responsive to magnetic flux, the detector means spacedly disposed from said driver coil and adapted to be disposed proximal to a surface of the pipe and not displaced axially along the pipe from said driver means more than one pipe diameter from a plane orthogonal to the axis of the pipe and common to said driver means;

(iii) displacement sensor means to output the distance of the inspection apparatus from a known location;

(iv) means for causing the inspection apparatus to move along the concrete pipe; and

(v) means for storing outputs corresponding to detector means and the displacement sensor means.

2. The inspection apparatus as claimed in claim 1, in which the detector means is a coil adapted to be disposed in relation to the concrete pipe with an axis parallel to the axis of the concrete pipe, and the output is a voltage induced in the coil by said magnetic flux.

3. The inspection apparatus as claimed in claim 1, in which the detector means is a pair of coils adapted to be disposed in relation to the concrete pipe such that each has an axis parallel to the axis of the concrete pipe, and the output is a voltage induced in the coils by said magnetic flux.

4. The inspection apparatus as claimed in claim 1, in which the detector means comprises at least one giant magnetoresistive sensor and the output is a change in resistance induced in the magnetoresistive sensor by said magnetic flux.

5. The inspection apparatus as claimed in claim 1, in which the detector means is a pair of giant magnetoresistive sensors and the output is a change in resistance induced in the said magnetoresistive sensors by said magnetic flux.

6. The inspection apparatus as claimed in claim 1, in which the detector means is a plurality of spacedly disposed giant magnetoresistive sensors, each oriented to be responsive to a magnetic flux of a corresponding region of each one such giant magnetoresistive sensor, and the output is a change in resistance induced in the said magnetoresistive sensors by said magnetic flux.

7. The inspection apparatus as claimed in claim 1 wherein said driver means comprises a coil having an axis that is oriented radial to the pipe.

8. The inspection apparatus as claimed in claim 7, in which the driver coil is located diametrically across the pipe from said detector means.

9. The inspection apparatus as claimed in claim 1, in which the driver coil is offset circumferentially from the detector means by an angle of at least 10 degrees.

10. The inspection apparatus as claimed in claim 1, in which the driver coil is offset around the circumference of the pipe from the detector means by a distance of at least one meter.

11. The inspection apparatus as claimed in claim 1 further including a magnetic shield interposed between the driver coil and the detector means.

12. The inspection apparatus of claim 1 mounted on a vehicle suited to movement through a pipeline.

13. The inspection apparatus of claim 1 additionally including means for converting the force of flow of a liquid in the pipeline into motion of the vehicle.

14. The inspection apparatus as claimed in claim 13, further including means for adjusting such means for converting the force of flow operative to slow or stop the vehicle when desired.

15. A method of detecting discontinuities in tensioning wires of a concrete pipe comprising:

(i) providing a driving signal to a driver having an axis oriented orthogonal to an axis of a concrete pipe and proximal to an inside surface thereof to generate an induced current in pre-stressing elements extending substantially circumferentially of the pipe;

(ii) providing a detector for producing an output responsive to a magnetic flux, the detector located in close proximity to an interior wall of a pipe and axially displaced not more than one pipe diameter of a plane orthogonal to the axis of the pipe and common to the driver,

(iii) moving the detector along the wall of the pipe; and

(iv) recording the output and the location of the detector as it moves.

16. A method of testing the tensioning wires of a pre-stressed concrete pipe along a length thereof using apparatus including magnetic flux production means spacedly disposed from magnetic flux detector means, said magnetic flux detector means adapted to be disposed proximal to a surface of a pipe, the magnetic flux production means producing a magnetic field in response to a driving signal and the detector means producing a detector signal in response to magnetic flux and locating means to indicate a location along said pipe and control means operatively connected to said locating means, to said magnetic flux production means and to said magnetic flux detector means, the method comprising performing the steps of:

(i) providing a driving signal of at least one frequency;

(ii) receiving a detector signal; and

(iii) recording the detector signal in relation to the frequency of the driving signal and the location indication over a range of locations traversed along a length of pipe.

17. The method of claim 16 further including the steps of:

(i) selecting at least one frequency, and

(ii) producing a trace for each selected frequency of the recorded detector signal in relation to the frequency of the driving signal and the selected location upon a display means.

18. The method of claim 17 wherein the display means is a display device.

19. The method of claim 17 wherein the display means is a printed graph.

20. The method of claim 16 wherein one frequency of driving signal is provided over the range of locations traversed.

21. The method of claim 20 further including the step of:

(i) providing a start location and an end location defining said range of locations along a length of pipe;

(ii) providing a single frequency of driving signal; and

(iii) traversing said range of locations advancing from the start location to the end location.

22. The method of claim 20 further including the steps of:

(i) providing a start location and an end location defining said range of locations along a length of pipe;

(ii) providing a range of frequencies of said driving signal;

(iii) traversing the range of frequencies at each location of said range of locations from the end location to the start location.

23. The method of claim 16 wherein the detector signal in relation to each frequency of the driving signal and the location indication is recorded at each location before traversing to a successive selected location.

24. A method of testing tensioning wires of a pre-stressed concrete pipe along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of a pipe to be tested in a spaced relationship to the other and axially disposed within one pipe diameter to the other, the magnetic flux production means producing a magnetic field in response to a driving signal and the detector means producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

(i) providing a driving signal of at least one frequency;

(ii) receiving a detector signal;

(iii) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal; and

(iv) recording the output representative of the detector signal in relation to the fundamental frequency and the location;

whereby at least one fundamental frequency is recorded over a range of locations traversed along a length of pipe.

25. The method of claim 24 including the step of producing an output representative of the amplitude and the phase of the detector signal expressed in Cartesian co-ordinates.

26. The method of claim 24 further includes the steps of displaying a first trace for at least one selected frequency of the recorded detector signal and the selected location upon a display means and displaying a second trace calculated from the Cartesian co-ordinates of the first trace based on a transposition angle alpha.

27. The method of claim 26 wherein the transposition angle alpha is selected to produce a mirror image excursion of portions of each trace over a range of interest.

28. The method of claim 27 wherein the display means is a display device.

29. The method of claim 27 wherein the display means is a printed graph.

30. The method of claim 24 wherein for each frequency of the driving signal, a range of locations are displayed.

31. The method of claim 24 wherein the length along the pre-stressed concrete pipe is a range of locations defined by a start location and an end location and the pipe is traversed from the start location to the end location for each selected frequency.

32. An inspection apparatus for detecting discontinuities in tensioning wire of a concrete cylinder, comprising:

(i) a driver coil adapted to be oriented with an axis orthogonal to an axis of a concrete cylinder to induce a current in a tensioning wire of a concrete cylinder in response to a driving signal;

(ii) means for producing a driving signal;

(iii) detector apparatus to produce an output responsive to a magnetic flux, said detector apparatus has an axis orthogonal to the axis of said driver coil and spacedly disposed there from, said detector coil adapted to be oriented proximal to a surface of said concrete cylinder and substantially in a plane orthogonal to an axis of the concrete pipe in common with the driver coil; and

(iv) filter means for producing an output signal representative of differences between the driving signal and the output produced by said detector apparatus.

33. The apparatus as claimed in claim 32, in which the detector apparatus is a coil adapted to be disposed with an axis parallel to the axis of the cylinder, and the output is a voltage induced in the coil by said magnetic flux.

34. The apparatus as claimed in claim 32, in which the detector apparatus is a pair of coils each adapted to be disposed with an axis parallel to the axis of the cylinder, and the output is a voltage induced in the coils by said magnetic flux.

35. The apparatus as claimed in claim 32, in which the detector apparatus is a giant magnetoresistive sensor and the output is a change in resistance induced in the magnetoresistive sensor by said magnetic flux.

36. The apparatus as claimed in claim 32, in which the detector apparatus is a pair of giant magnetoresistive sensors and the output is a change in resistance induced in the said magnetoresistive sensors by said magnetic flux.

37. The apparatus as claimed in claim 32, in which the detector apparatus is a plurality of spacedly disposed giant magnetoresistive sensors, each oriented to be responsive to a magnetic flux of a corresponding orthogonal axis to each other one such giant magnetoresistive sensor, and the output is a change in resistance induced in each said magnetoresistive sensors by said magnetic flux.

38. The apparatus as claimed in claim 32 wherein said driver means comprises a coil adapted to be oriented with an axis that is oriented radial to the cylinder.

39. The apparatus as claimed in claim 38, in which the driver coil is spacedly disposed from said detector apparatus to be adapted to be positioned diametrically across the concrete cylinder from said detector apparatus.

40. The apparatus as claimed in claim 32, in which the driver coil is spacedly disposed from said detector apparatus to be adapted to be positioned circumferentially offset from the detector apparatus by an angle of at least 10 degrees.

41. The apparatus as claimed in claim 32, in which the driver coil is spacedly disposed from said detector apparatus to be positioned circumferentially offset from the detector apparatus by a distance of at least one meter.

42. The apparatus as claimed in claim 32 further including a magnetic shield interposed between the driver coil and the detector apparatus.

43. The apparatus as claimed in claim 32 further including:

(i) displacement sensor means to produce an output representative of at least one distance of the detector apparatus a from a known location;

(ii) means to cause the detector apparatus to move; and

(iii) means for storing outputs derived from the output of the filter means and said displacement sensor means.

44. The apparatus of claim 32 wherein said filter apparatus includes a multiplier and a low pass filter.

45. The apparatus to claim 32 wherein said filter apparatus includes a lock-in amplifier.

46. The apparatus of claim 32 mounted on a vehicle suited to movement along a pipeline.

47. A method of detecting discontinuities tensioning wires a concrete cylinder comprising:

(i) providing a driving signal to a driver coil means having an axis oriented orthogonal to an axis of a concrete cylinder to generate induced current in pre-stressing elements extending substantially circumferentially around the cylinder;

(ii) providing a detector proximal to a surface of the concrete cylinder and spacedly disposed from said driver means along said axis of said driver coil means, the detector to produce an output responsive to a magnetic flux;

(iii) filtering the output of the detector relative to the driving signal; and

(iv) recording the filtered output and the location of the detector.

48. A method of testing the tensioning wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each proximal to a surface of a cylinder and in a spaced relationship to each other, the magnetic flux production means to produce a magnetic field in response to a driving signal and the detector means to produce a detector signal in response to magnetic flux and locating means to indicate a location along said cylinder and control means operatively connected to said locating means, to said magnetic flux means and to said detector means, the method comprising performing the steps of:

(i) providing a driving signal of at least one frequency;

(ii) receiving a detector signal;

(iii) filtering the received detector signal relative to the driving signal;

(iv) receiving a location indication; and

(v) recording the filtered detector signal, the frequency of the driving signal and the location indication over a range of locations traversed along a length of cylinder.

49. The method of claim 48 further including the steps of selecting at least one frequency and displaying a trace for each selected frequency of the recorded detector signal in relation to the frequency of the driving signal and the selected location upon a display means.

50. The method of claim 49 wherein the display means is a display device.

51. The method of claim 49 wherein the display means is a printed graph.

52. The method of claim 48 wherein one frequency of driving signal is provided over the range of locations traversed.

53. The method of claim 52 further including the step of:

(i) providing a start location and an end location defining said range of locations along a length of cylinder;

(ii) providing a single frequency of driving signal; and

(iii) traversing said range of locations advancing from the start location to the end location.

54. The method of claim 52 further including the steps of:

(i) providing a start location and an end location defining said range of locations along a length of cylinder;

(ii) providing a range of frequencies of said a driving signal;

(iii) traversing the range of frequencies at each location of said range of locations from the end location to the start location.

55. The method of claim 48 wherein the filtered detector signal in relation to each frequency of the driving signal and the location indication is recorded at each location before traversing to a successive selected location.

56. A method of testing the tensioning wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of the cylinder in a spaced relationship to the other and axially disposed not more than one cylinder diameter from the other, the magnetic flux production means for producing a magnetic field in response to a driving signal and the detector means for producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

(i) providing a driving signal of at least one frequency;

(ii) receiving a detector signal;

(iii) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal; and

(iv) recording the output representative of the detector signal in relation to the fundamental frequency, the fundamental frequency and the location;

whereby at least one fundamental frequency is recorded over a range of locations traversed along a length of cylinder.

57. The method of claim 56 wherein the step of producing an output representative of the amplitude and the phase of the detector signal comprises forming Cartesian co-ordinates X and Y.

58. The method of claim 56 further including the steps of displaying a first trace for at least one selected frequency of the recorded detector signal and the selected location upon a display means and displaying a second trace calculated from either the X or Y co-ordinates of the first trace based on a transposition angle alpha.

59. The method of claim 58 wherein the transposition angle alpha is selected to produce a mirror image excursion of portions of each trace over a range of interest.

60. The method of claim 59 wherein the display means is a display device.

61. The method of claim 59 wherein the display means is a printed graph.

62. The method of claim 56 wherein for each frequency of the driving signal, a range of locations are displayed.

63. The method of claim 56 wherein the length along the pre-stressed concrete cylinder is a range of locations defined by a start location and an end location and the cylinder is traversed from the start location to the end location for each selected frequency

64. A method of testing the tension wires of a pre-stressed concrete cylinder along a length thereof using apparatus including magnetic flux production means and magnetic flux detector means each disposed proximal to a surface of the cylinder, the magnetic flux production means for producing a magnetic field in response to a driving signal and the detector means for producing a detector signal in response to magnetic flux, location indication means and control means operatively connected to said location indication means, to said magnetic flux means and to said detector means, the method comprising:

(i) providing a driving signal of at least one frequency;

(ii) positioning the detector means in relation to the magnetic flux production means, each said detector means and the magnetic flux production means axially disposed not more than one cylinder diameter to the other;

(iii) receiving a detector signal;

(iv) producing an output representative of the detector signal corresponding to the in-phase and quadrature components of the detector signal in relation to the fundamental frequency of the driving signal; and

(v) recording the location of the detector means and output representative of the detector signal in relation to the fundamental frequency, the fundamental frequency and the location of a deter;

whereby at least one fundamental frequency is recorded over a range of locations traversed by said detector means along a length of a pre-stressed concrete cylinder.

65. The method of claim 64 wherein producing an output representative of the amplitude and the phase of the detector signal comprises Cartesian co-ordinates X and Y.

66. The method of claim 64 further includes the steps of producing a first trace for at least one selected frequency of the recorded detector signal and the selected location upon a display means and producing a second trace calculated from either the X or Y co-ordinates of the first trace based on a transposition angle alpha.

67. The method of claim 66 wherein the transposition angle alpha is selected to produce a mirror image excursion of portions of each trace over a range of interest.

68. The method of claim 67 wherein the display means is a display device.

69. The method of claim 67 wherein the display means is a printed graph.

70. The method of claim 64 wherein for each frequency of the driving signal, a range of locations of said detector means with respect to the axis of the concrete cylinder are displayed.

71. The method of claim 64 wherein the length along the pre-stressed concrete cylinder is a range of locations defined by a start location and an end location and the cylinder is traversed by said detector means from the start location to the end location for each selected frequency.

72. Apparatus for detecting discontinuities in a spirally wound metallic pre-stressing reinforcements embedded the wall of a concrete pipe or substantially cylindrical fluid containment structure having a longitudinal axis, comprising:

(i) a detector oriented to lie along the wall surface of said concrete pipe or structure to be monitored, said detector being capable of detecting magnetic flux flowing in a direction parallel to the longitudinal axis of the pipe or structure, means for causing the detector to move along the surface of such pipe or structure;

(ii) means for determining at least one of the location of the detector or the distance it has moved from a known original location;

(iii) means for recording the magnetic flux recorded by the detector and recording it in association with the location of the detector when such flux was detected or the distance that the detector has moved from an original known location when such flux was detected.

73. Apparatus as claimed in claim 72, in which the detector is a coil having an axis parallel to the longitudinal axis of the pipe, and the magnetic flux is detected as a voltage induced in the coil.

74. Apparatus as claimed in claim 72, in which the detector is a GMR sensoe.

75. Apparatus as claimed in any of claims 72-74, including means for generating a periodically varying current in the spirally wound metallic pre-stressing reinforcements.

76. Apparatus as claimed in any of claims 72-74, additionally comprising a driver coil having an axis which is radial to the longitudinal axis, for generating such periodically varying current.

77. Apparatus as claimed in claim 76, in which the driver coil is located diametrically across the pipe or structure from the detector.

78. Apparatus as claimed in claim 76, in which the driver coil is located diametrically across the pipe or structure from the detector, but axially offset therefrom a distance not more than one diameter of the pipe or structure.

79. Apparatus as claimed in claim 75, in which the driver coil is offset circumferentially from the detector on the pipe or structure by an angle of at least 90 degrees.

80. Apparatus as claimed in any of claims 75-79, having a shield for magnetic flux located in line of sight between the detector and the driver coil.

81. Apparatus comprising the apparatus of any claims 72-80, where the pipe or structure is a pipeline and the apparatus is mounted on a vehicle suited to movement through a pipeline.

82. Apparatus of claim 81 additionally including means for transmitting the force of flow of liquid in the pipeline into forward motion of the vehicle.

83. Apparatus as claimed in claim 82, additionally comprising means for adjusting such means for transmitting the force of flow, whereby to slow or stop the vehicle when desired.

84. A method of detecting discontinuities in spirally wound metallic pre-stressing elements of a concrete pipe having such elements which comprises:

(i) providing a detector coil which has its axis parallel to the axis of the pipe, and which is of a diameter less than one quarter of the diameter of the pipe,

(ii) placing the detector coil in close proximity to the interior wall of the pipe,

(iii) generating a periodically varying induced current in the pre-stressing elements,

(iv) moving the detector coil along the wall of the pipe and

(v) recording the distance moved or the location of the detector coil, and the induced voltage or current sensed by the detector coil as it moves.

85. A method as claimed in claim 84, in which the periodically varying induced current is generated by a driver coil orthogonal to the detector coil.

86. A method as claimed in claim 84 or claim 85, in which the periodic current is a sinusoidal waveform.

87. A method as claimed in claim 84 or claim 85, in which the periodic current has a sawtooth waveform.

88. A method as claimed in claim 84 or claim 85, in which the periodic current has a square waveform.