Electricity: measuring and testing – Magnetic – Magnetic sensor within material
Patent
1979-05-09
1981-09-29
Strecker, Gerard R.
Electricity: measuring and testing
Magnetic
Magnetic sensor within material
324233, 324241, G01N 2772, G01N 2782, G01R 3312
Patent
active
042925894
ABSTRACT:
Casing inspection apparatus and method are disclosed for determining defects and other anomalies in ferromagnetic oil well casing. The inspection apparatus utilizes a pair of coaxial transmitter coils for generating an alternating magnetic field in the casing thereby inducing circumferential currents in the casing wall. These circumferential currents and the magnetic field associated with the currents are perturbed by corrosion, holes, and other anomalies both inside and outside the casing wall. Differential receiver coils are urged in proximity with the casing wall to generate a differential receiver signal in response to such perturbations in the magnetic field. The differential receivers are provided with three coils serially connected and having N, 2N and N winding turns respectively. The windings of the coils are disposed in adjacent relationship to one another and wound in a direction opposite to the adjacent winding. The casing inspection apparatus achieves enhanced sensitivity to small defects and reduced sensitivity to magnetic anomalies by processing both the amplitude and phase components of the receiver signal.
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Schlumberger Technology Corporation
Snow Walter E.
Strecker Gerard R.
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