A technology of full perimeter inspection for steel pipeline without removing cladding

Abstract

This study proposes a rotating excitation magnetic field detection method to identify in-service cladding steel pipeline damage. A ring of uniformly arranged excitation coils generates excitation magnetic fields under the action of a three-phase current, which synthesize in the pipe as a rotating magnetic excitation field based on the principle of vector synthesis. Tunneling magneto-resistive (TMR) sensors work as detection probes for measuring magnetic induction strength. The induced current flows circularly in the pipe's body under the influence of a rotating excitation field. Therefore, this excitation method has a high sensitivity to defects in different length directions and can detect damage information in the whole circumference of the pipe body. The TMR sensors are uniformly arranged along the pipe's rim and measure the magnetic field in the radial direction with high sensitivity and low background noise (10 pT/Hz@1 kHz). The finite element method investigated the operating principle and performance of two excitation coils probe structures. The specimen probe and signal acquisition setup was developed and examined, with which artificial damages in the pipeline with cladding were inspected. The test result indicates that the proposed probe can penetrate the surface cladding of the pipe, effectively identifying defects in the pipeline.