Aiming at the problem of defects detection of steel pipeline, a harmonic detection system was developed based on electromagnetic principle, and the target signal identification algorithm was studied. The Advanced RISC Machine (ARM) Cortex-M3 was adopted to design digital adjustable harmonic excitation source, and its effective output power can up to 70 W. The Field Programmable Gate Arrays (FPGA) and ARM Cortex-M4 were introduced to design 15 channels high speed data collector, which parallel local-storage rate of each channel can reach 4.7 kHz. The electromagnetic focusing excitation array and Tunnel Magneto Resistance (TMR) sensors array were constructed to improve the spatial resolution of the detection system. Meanwhile, the system also integrated GPS positioning and LCD real-time display functions. Furthermore, the algorithm combining Empirical Mode Decomposition (EMD) and variable-scale Stochastic Resonance (SR) was proposed to process signal and enhance the targets. The effectiveness of the instrument and algorithm are well verified in both simulation and experiment. The results show that this method has higher integration and better detection effect, which provides a novel method for non-contact detection of metal material defects and is suitable for engineering applications.

In this study, a harmonic magnetic field detection technology is proposed in order to detect the damage of an in-service coated steel pipeline. Based on the electromagnetic theory and magnetic field detection principle integrated with magnetic focusing technology, an array consisting of focusing detection probe and harmonic magnetic field detection system was designed. Numerical simulations for different coil structures was performed by finite element simulation technique to explore the focusing performance of designed coil structure. The feasibility of the detection probe and harmonic magnetic field detection technology was verified by experimental results and numerical simulations. The results of this study show that the proposed method can provide excellent information about the full wall thickness by penetrating the cladding over the surface of pipeline and effectively identify the outer wall defects and the inner wall corrosion. (C) 2020 Elsevier Ltd. All rights reserved.

Harmonic eddy current magnetic field inspection, as one of pipeline nondestructive inspection technology, can be accurately and efficiently used to estimate the damage of buried steel pipeline. Based on the principle of harmonic eddy current magnetic field detection, a theory model of double frequencies alternating excitation was established, and a non-contact coil array detection probe was also designed. An indoor experimental platform was built to proceed experimental study on the differences in magnetic induction intensity distribution for various pipeline defect species, and the variation in magnetic induction intensity for different excitation frequencies and input voltages. Results showed that change in resistivity due to the pipeline defect causes a nonuniform current distribution that distorts the induced magnetic field, resulting significant increase in the magnetic induction intensity; While moving the probe along the surface of the pipeline, better detection results can be achieved for various defect species with greater defect depth and smaller angular orientation between defect trend and moving direction; Similarly a robust change in the magnetic induction intensity can be observed with low signal frequency of harmonic power supply and greater input voltage of detection probe. The researches done prove that harmonic eddy current magnetic field inspection can effectively realize the nondestructive damage detection of buried steel pipeline.