Evaluation of Lift-Off Effect on Metal Testing with Non-Conductive Coating by Using Eddy Current Testing Technique

This study aims to develop an Eddy current testing (ECT) probe that generates Eddy current signals when a coil is placed above each magnetic (stainless steel 304) and non-magnetic (aluminium 6061) metal testing, with nonconductive coating and the presence of lift-off height, i.e., 0, 2.5, 5.0, 7.5, and 10.0 +/- 0.5 mm. Then this test is conducted with varying thicknesses, i.e., 1.5, 3.0, and 5.0 +/- 0.5 mm, and an artificial defect, i.e., 10, 20, and 30 +/- 0.5 mm, engraved on the metal testing. The coil probe is a rod-shaped solenoid coil designed with an iron core with 65 mm length, 5 mm2 area, and 200 N turns. It demonstrates how the rod-shaped solenoid coil may be used to detect various surface defects in aluminium 6061 (Al 6061) and stainless steel 304 (SS304). The optimal frequencies for Al6061 were 7.838 MHz, and SS304 metal was 7.956 MHz. In conclusion, the output voltage signals for each coated metal testing decreases as the lift-off height increases with increasing the thickness of metal. Therefore, as compared the magnetic and non-magnetic materials it shows the differences in the output voltage. Hence, the ECT technique in this study can detect surface defects appropriately for magnetic and non-magnetic materials.