Eddy Current Testing – ECT

Introduction:

Eddy current testing is a non-destructive material examination technique frequently used to detect near-surface defects of conductive materials. ECT works on the principle of electromagnetic induction to identify surface cracks, measure approximate dimensions of cracks, measure metal sheet thickness, identify corrosion in metal substrates with coatings, etc. It is widely used in aerospace and other manufacturing industries for inspection and quality control to ensure safe operation and avoid expensive equipment and component failure.

A simple single-element ECT probe consists of a copper coil that produces a magnetic field when excited with an alternating current. When this probe comes within proximity of a conductive material, its magnetic field induces currents in the material known as eddy currents. Industrial ECT probes have multiple small coils placed at various orientations, which dictates the probes’ sensitivity and applicability. ECT probes measure tiny variations in the eddy currents’ path with high sensitivity and detect even small cracks as they scan large surfaces of conductive materials. Handheld field probes and large fixed systems are available for varying applications making ECT a versatile tool for quick onsite inspections and complex laboratory studies. Remote Field Testing (RFT), Flux Leakage, and Barkhausen Noise are other testing methods that use the principle of eddy current testing.

Other eddy current testing procedures such as Eddy current array (ECA) were created with varying degrees of success to get around some of the drawbacks of traditional ECT. The fundamental principles of both eddy current arrays (ECA) and traditional ECT are the same. With the use of ECA technology, it is possible to electronically control the topology—an array of coils (many coils)—that produces a sensitivity profile appropriate for the target flaws. In order to prevent mutual inductance between the individual coils, data capture is accomplished by multiplexing the coils in a certain pattern. 

Video 01: Eddy Current Testing (ECT)