Defect detection in stainless steel tubes with AMR and GMR sensors using remote field eddy current inspection

The purpose of this paper is to compare the performance of the giant magneto-resistor (GMR) and anisotropic magneto-resistor (AMR) sensors for remote field eddy current testing in stainless steel tubes. Two remote field eddy current probes were built to compare detection and characterization capabilities in standard defects like longitudinal and transverse defects. Both probes include a coil to produce a sinusoidal magnetic field that penetrates the tube wall. Each probe includes a detector with GMR and AMR sensors, where each sensor has four magneto-resistive elements configured in a Wheatstone bridge. Each sensor needs to be biased differently to operate in the high sensitivity linear mode. The description of the measurement system used to detect defects is present in the paper. For the choice of the detector optimal position, numerical simulation and experimental measurements were performed. For comparison of these sensors in defect detection using remote field eddy current testing, the experimental measurements were performed under the same conditions. The results are presented and discussed in the paper.