Quantitative Nondestructive Evaluation of the Crack on the Austenite Stainless Steel Using the Induced Eddy Current and the Hall Sensor Array

Nondestructive evaluation (NDE) has been effective in the prediction and evaluation of cracks on the surface of structures. Austenite stainless steel such as SUS304 and SUS316 is a paramagnetic metal with delta -ferrite structure. Small amount of partial magnetization is generated in the austenite stainless steel due to the final heat treatment and the mechanical working. The MOI (magneto-optical/eddy current imaging) was developed to inspect fatigue cracks and corrosions. But the surface cracks on the partially magnetized paramagnetic metals, such as austenite stainless steel, are difficult to inspect because the magnetic domains were saturated by external magnetization of the delta -ferrite. In this paper, the magnetic camera with the 64 arrayed Hall sensors by matrix (sensor matrix) was developed to confirm the real time inspection and quantitative nondestructive evaluation (QNDE). As the result, QNDE algorithm was proposed by using single sensor scanning, and the algorithm was introduced in QNDE by sensor matrix. Also, the cracks were inspected in the real time by sensor matrix, which were arrayed with 3.5 mm spatial resolution in square.