How ECT Works
Eddy current testing induces electrical currents in a conductive material; a crack disturbs these currents and the instrument detects the change. It needs no couplant and may work through suitable non-conductive coatings when lift-off and surface condition are controlled.
Ideal Applications
ECT is especially useful for:
- Fatigue crack detection on EWPs and cranes
- Weld inspection through paint
- Bolt hole and fastener inspection
- Fast screening of many components
Limitations
ECT needs an electrically conductive test object and is most sensitive near the surface. Lift-off, coating thickness, edges, fasteners, curvature, weld geometry, conductivity and permeability can change the signal or mimic an indication. A response is interpreted against calibration and the inspection procedure; it is not automatically a rejectable crack.
Choosing Between Methods
ECT can complement MPI or PT for surface-breaking cracking, while UT may be more appropriate when internal coverage or thickness information is required. The method should be selected for the material, access and likely defect rather than for speed alone.