Eddy Current Testing (ECT) works on the principle of electromagnetic induction. In ECT a probe is excited with sinusoidal alternating current to induce eddy current in an electrically conducting material such as stainless steel, aluminium etc. The change in coil impedance that arises due to distortion at regions of discontinuities and associated magnetic flux leakage is measured. This is a surface technique and can readily detect very shallow surface defect and sub-surface defects. ECT is a simple, high-speed, high sensitive, versatile and reliable NDT technique and is popularly used in many engineering industries.
Rapid growth in performance requirements of modern automobiles has brought about a more stringent demand for quality control of automotive materials and components. Eddy-current inspection can be an effective way to ensure these requirements are met
Primary applications are non-destructive verification of material properties resulting from heat treatment and alloy processes and detection of surface cracks and flaws resulting from rolling, forming, machining and finishing and heat-treat processes
The cracks in parent material are real threat for the reliability of a structure, as they can rapidly grow to cause failures of structural integrity. On other hand, for welds, there is a need to detect surface breaking defects on weld beads as well as transition and heat affected zones.
For Ferro- magnetic materials e.g. carbon steel, generally magnetic particle inspection is used. However, eddy current inspection offers a number of advantages;