Subsurface crack detection in steel plate using differential transient eddy current oscillations method

Steel is a vital structural material used in large-scale industries in the energy sector, particularly in oil, gas, and power plants. The long-term use of metal structures, such as pipelines, may be affected by corrosion over time due to harsh operating conditions and environmental factors, resulting in a reduction in pressure handling capacity due to wall loss. This can lead to hidden fissures that are difficult to detect. This study uses Transient Eddy Current Oscillations (TECO), an electromagnetic Non-destructive Testing (NDT) approach to detect sub-surface cracks in stainless steel. Unlike the standard Eddy Current Testing (ECT), TECO employs decay of oscillations from an LC circuit at the natural resonance frequency. A differential probe with two Hall sensors used to detect the resultant magnetic field caused by induced eddy currents. A stainless steel test specimen with artificial sub-surface cracks from 1 to 2.5 mm deep, which were created by Electro Discharge Machining (EDM). From the results, the crack depth is interpreted in terms of signal amplitude, decay rate and Teager energy as features for detecting sub-surface flaws, and this interpretation is confirmed by FEM results.