Eddy Current Probe for Inspection of Steel Tubes Based on Rotating Field Principle

Eddy current probes are ubiquitous in monitoring of industrial tubing such as oil well casings, pipelines or heat exchangers in order to ensure their structural integrity and safety. State-of-the-art configurations of the eddy current probes are coil arrays and mechanically rotating probes. The increased sensitivity of these probes to defects oriented in angular direction and their imaging capability come at the price of complicated interface and acquisition circuitry, and unreliability due to mechanically moving parts. An alternative design, proposed previously, is based on the rotating magnetic field and a three-coil three-phase transmitter. The signal from such a probe depends on the angular position of a defect and this could enable imaging of the wall condition. In this paper, we describe a laboratory demonstrator of a rotating field eddy current sensing system for inspection of oil well casings. Furthermore, we present the experimental results that corroborate the analytical model of the transmitter inside the steel tube and the dipole-based model of small defects.