Magnetic Flux Leakage Testing for Back-side Defects Using a Tunnel Magnetoresistive Device

Magnetic non-destructive testing is limited to surface inspection, however demand for the detection of deep defects is increasing. Therefore, we developed a magnetic flux leakage (MFL) system using a tunnel magnetoresistive (TMR) device that has high sensitivity and wide frequency range in order to detect deep defects. Using the developed system, back-side pits of steel plates having different depth and diameter were measured and 2D images were created. Moreover, we analyzed the detected vector signal with optimized phase data. As a result, the developed MFL system can detect a defect that has a wall thinning rate of more than 56 % of 8.6 mm thick steel plates. Furthermore, the defect’s diameter size was estimated by spatial signal change. Keywords-MFL; magnetic imaging; TMR device; LowFreaquency field; back-side pit.