High-Speed Inspection Method Fusing Pulsed Eddy Current and Magnetic Flux Leakage

High-speed inspection of defects on thick-wall steel pipes is important to pipeline inline inspection (ILI) in the oil and gas industry. Traditional inspection methods are limited by the main challenges of inspection principle, sensor design and instrument implementation, resulting in these methods hardly applicable to practical high-speed pipeline ILI. This paper proposes a novel high-speed inspection method fusing pulsed eddy current (PEC) and magnetic flux leakage (MFL) to detect sub-surface defects. When the ferromagnetic steel pipes are magnetized by an applied strong DC magnetic field to saturation status, the existence of sub-surface defects will cause leaked magnetic fields and non-uniform permeability distributions, which can be measured by Hall effect sensors and PEC coil sensors, respectively. A fusion inspection probe containing four-channel Hall effect sensors and two-channel PEC coil sensors is designed and developed here for measuring three-axis MFL signals and 2-D PEC signals simultaneously. A novel high-speed pipeline inspection gauge (PIG) with a sensor array containing 45 fusion inspection probes is developed for field testing to validate the proposed method that achieved superior detection capability in high inspection speed.