Proposal of defect inspection method of steel plate by full-wave rectified magnetic field

The large-diameter steel pipes are often used in petrochemical plants. In this large-diameter steel pipe, there are many cases where corrosion in the steel pipe is inspected from the outside of the steel pipe. In particular, there is a demand for a method for detecting defects inside or outside the steel pipe from the outer side of the steel pipe at high speed. Therefore, the electromagnetic inspection method is useful for detecting these defects. In the electromagnetic inspection method, using both static (DC) magnetic field and alternating (AC) magnetic field is proposed for inspecting inner side defects as well as outside defects. On the other hand, the Fourier series expansion of the full-wave rectified wave of the stationary AC magnetic field shows that it is a composite of the DC component and the AC component due to the cosine wave. Therefore, in this research, an inspection method using full-wave rectified AC magnetic field is proposed for inspecting inner side defects as well as surface defects. In this paper, the usefulness of the proposed method is demonstrated by electromagnetic field analysis using the “play model” that takes into account minor loop magnetic properties. In addition, a verification experiment is also carried out.