Method and apparatus for the detection of pipeline holidays

• US 4,390,836 A
• Filed: 08/11/1980
• Issued: 06/28/1983
• Est. Priority Date: 08/11/1980
• Status: Expired due to Term

• Current Assignee: Marathon Oil Company (Marathon Oil Corporation)
• Original Assignee: Marathon Oil Company (Marathon Oil Corporation)
• Inventors: Bruce, Charles R., Johnson, Irvin D.
• Primary Examiner(s): Strecker, Gerard R.
• Application Number:
  US06/177,156
• Time in Patent Office: 1,051 Days
• Field of Search: 324/52, 324/54, 324/67, 324/72, 324/326, 324/71 R
• US Class Current: 324/557
• CPC Class Codes: G01R 31/58 Testing of lines, cables or conductors testing of electric windings G01R31/72
• CPC Class Codes: G01V 3/06 using ac

Abstract

A method and apparatus are provided for detecting and locating holidays in an insulating coating of a subterranean pipeline. An alternating current is induced in the portion of the pipeline being surveyed. The pipeline is tracked by sensing the normal electromagnetic field generated by the current flowing in the pipeline. Leakage current indicative of the location and magnitude of a holiday in the pipeline coating is sensed by a pair of coil members adapted to be located above the ground on opposite sides of a vertical plane including the longitudinal axis of the pipeline with the central axes of the coil members being oriented generally parallel to the central axis of the pipeline, whereby an electrical current signal is induced in the pair of coil members by an electromagnetic field generated by the leakage current. The electrical current signal is displayed to provide an indication of the location and magnitude of the holiday.

Claims

1. Apparatus for detecting and locating a holiday in an insulating coating of a subterranean electrically conductive pipeline comprising:

an alternating electrical current source electrically connected to an electrically conductive pipeline having an insulating coating for inducing an alternating electrical current flowing in a direction parallel to the central axis of the pipeline in at least a portion of the pipeline,

a holiday current sensing means for sensing the presence of a holiday in the insulating coating of the pipeline and for producing a signal representative of electrical current flowing in a direction normal to the central axis of pipeline through the holiday, the holiday current sensing means comprising a pair of coil members adapted to be located above the ground approximately an equal distance from a vertical plane including the central axis of the pipeline with the central axes of the coil members being oriented generally parallel to the central axis of the pipeline, whereby an electrical current signal is induced in the pair of coil members by an electromagnetic field generated by current flowing through the holiday,

a first display means for displaying the signal induced in the pair of coil elements, the signal being representative of the presence and magnitude of the holiday,

a mobile support means for supporting the pair of coil members and moving the pair of coil members relative to the pipeline, and

a pipeline sensing means for sensing the location of the pipeline and for producing a signal representative of the relative position of the pipeline sensing means and the pipeline, the pipeline sensing means comprising a first electrical current sensing means mounted on the mobile support means for sensing the phase and magnitude of the alternating current flowing axially in the pipeline and for providing a first signal representative thereof, a second electrical current sensing means mounted on the mobile support means for sensing the relative location of the second sensing means and the pipeline and for providing a second signal representative thereof, and phase comparison means for comparing the phase relationship of the first and second signals, the first electrical sensing means comprising a first coil member adapted to be oriented over the pipeline with its central axis located horizontally to the ground and perpendicularly to the central axis of the pipeline whereby a first electrical signal representative of the phase and magnitude of current flowing axially in the pipeline is induced in the first coil member by a normal electromagnetic field generated by the current flowing axially in the pipeline;

the second electrical current sensing means comprising a second coil member adapted to be oriented over the pipeline with its central axis located vertically to the ground and perpendicularly to the central axis of the pipeline, whereby a second electrical current signal representative of the relative location of the second coil member and the pipeline is induced in the second coil member by the normal electromagnetic field generated by current flowing axially in the pipeline.

2. The apparatus of claim 1 wherein the phase comparison means comprises a zero cross detection means for detecting the zero voltage points of the first electrical current signal and providing an output signal representative thereof;

and a first phase lock amplifier for receiving the output signal from the zero cross detection means and the second electrical current signal, and for providing an output signal representative of the relative phase condition of the zero cross detection means output signal and the second electrical current signal, and of the magnitude of the second electrical current signal.

3. The apparatus of claim 2 which further comprises a second display means for displaying the output signal from the first phase lock amplifier.

4. The apparatus of claim 3 wherein the mobile support means is guidable in response to the second display means.

5. The apparatus of claim 3 wherein the second display means comprises a center zero steering meter.

6. The apparatus of claim 2 which further comprises selective amplification means for selectively amplifying a relatively narrow band of frequencies from the electrical current signal of the holiday current sensing means about a mid-band frequency value determined by the output signal and for supplying the selectively amplified signal to the first display means.

7. The apparatus of claim 6 wherein the selective amplification means comprises a second phase lock amplifier.

8. The apparatus of claim 7 wherein the first display means comprises a chart recorder.

9. The apparatus of claim 8 wherein the flow of paper in the chart recorder is driven in response to the distance traveled by the mobile support means.

10. A method of detecting and locating a holiday in an insulating coating of a subterranean electrically conductive pipeline comprising:

inducing an alternating electrical current in at least a portion of the pipeline,

orienting a pair of coil members on opposite sides of a vertical plane including the longitudinal axis of the pipeline in generally longitudinally parallel relationship relative to the pipeline,

moving the pair of coils through an electromagnetic field generated by electric current flowing in a direction normal to the central axis of the pipeline through a holiday in the insulating coating of the pipeline whereby an electrical current signal is induced in the pair of coil members representative of the presence and magnitude of the holiday,

displaying the electrical current signal, and

sensing a normal electromagnetic field generated by the current flowing axially in the pipeline, determining the relative relationship between the pair of coil members and the pipeline from the sensed normal electromagnetic field and then guiding the pair of coil members through the electromagnetic field generated by electrical current flowing radially through the holiday in response to the sensed normal electromagnetic field.