Method and apparatus for the detection of pipeline holidays

Claim 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.

Claim 11

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.

Claim 12

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.