Surface-breaking flaw detection in mild steel welds using quantum well hall effect sensor devices

With growing industrial interest in Non-Destructive Evaluation (NDE) applications of Quantum Well Hall Effect (QWHE) sensors, a study was conducted to quantitatively determine the detection capabilities and general performances of low frequency QWHE imaging for surface-breaking flaws and their comparison with Magnetic Particle Inspection (MPI), Eddy Current Testing (ECT) and Alternating Current Field Measurement (ACFM). In this study, a probe consisting of a QWHE sensor, illuminating electromagnet and sensor circuitry was controlled using an automated XY scanner with a measurement step of 250 μm to simulate an integrated array of QWHE sensors of 250 μm pitch. This probe applied a 3 mT, 100 Hz frequency magnetic field to map the surface magnetic field and Magnetic Flux Leakage (MFL) response of five bespoke dressed mild steel weld samples. These samples provided 15 surface-breaking flaws of varying length from 3 to 11 mm; mainly longitudinal toe and center-line cracks which are representative of typical requirements of our industrial partners. The same samples were also subjected to MPI, ECT and ACFM provided by leading industrial companies using their own qualified personnel, equipment and procedures. The outcomes and performance of each NDE technique including QWHE imaging were then compared and evaluated.