Rotating alternating current field measurement testing system with TMR arrays for arbitrary-angle crack on nonferromagnetic pipes

Nonferromagnetic pipes are widely used in power plants such as fluid transportation and heat exchanger devices. Due to the severity of the environments, including corrosion, high temperature, etc, they are subject to surface arbitrary-angle cracks. In view of this background, this paper proposed a rotating alternating current field measurement (RACFM) testing system for arbitrary-angle cracks on nonferromagnetic pipes. The RACFM pipe detection model is established and the unidirectional excitation coil and the orthogonal excitation coils are simulated separately. The testing system and the probe with tunnel magneto resistance sensor arrays and flexible orthogonal excitation coils are built to detect cracks at different angles on the pipe. The simulation and experimental results reveal that the RACFM detection system has high sensitivity for arbitrary-angle cracks on the outer surface of the pipe, and it can effectively measure the lengths and angles of the cracks.