Defect Detection in the Dead Zone of Magnetostrictive Sensor for Pipe Monitoring

Abstract

Magnetostrictively transmitted and received guided waves can detect long distances from a single sensor position without a couplant. They are widely used in nondestructive testing and in testing the structural integrity of piping. If the guided waves reflected from a defect return to the sensor before the sensor excitation process has finished, the guided waves will then be submerged under the excited guided waves. This creates a dead zone in the guided wave detection. In this article, far-field eddy current testing is used to reduce the dead zone of the magnetostrictively excited guided wave detection. Both magnetostrictively excited guided waves and the far-field eddy current detection method are based on the principle of electromagnetic induction. The main components of the magnetostrictive sensor are a static magnetic field and coils; these components can also be used to realize far-field eddy current testing without the need for additional sensors. The defects located at the far end of the pipe are detected using the guided wave signal. The defects located in the guided wave testing dead zone are detected using the eddy current signal. Through a combination of simulation analysis and experimental verification, it is demonstrated that far-field eddy current detection can reduce the dead zone and enhance the reliability of the magnetostrictively excited guided wave detection.