Eddy current method and apparatus for inspecting ferromagnetic tubular members
US4292589A · kind A · utility
Assignee
Inventor
Key dates
| Filing date | May 9, 1979 |
| Grant date | Sep 29, 1981 |
| Priority date | — |
| Expiry date | May 9, 1999 |
Classification
- Technology area (CPC G)Physics
- CPC primaryG01N27/9046
- WIPO fieldMeasurement
- WIPO sectorInstruments
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.
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.