Eddy Current Testing: Profiled eddy current probes for complex shape inspection

The Eddy Current Testing (ECT) method forms part of the Electromagnetic Testing methods (ET) and is used to detect surface and subsurface discontinuities in conductive materials. Testing of conductive samples is also possible through limited thickness non-conductive coatings or non-reinforced rubber lining. Complex shapes and hard to reach surfaces are difficult to inspect, since the orientation of the probe relative to the surface constantly varies. Probe shoes and other alternatives are available that can limit the probe lift off or probe ‘wobble’, however with various degrees of success. This paper discuss the use of profiled eddy current probes to inspect complex shapes such as turbine blade steeples, generator rotor bodies, gear teeth (girth and pinion gears), etc. The probes are designed according to the component profile and thus aim to improve the detection and characterization of indications, while limiting the effect of lift-off, probe wobble or other factors related to the probe manipulation or magnetic coupling with the test sample. Even the depth of indications can be determined under certain conditions viz. if suitable calibration blocks and representative reference samples are available.