電子走査形渦流探傷法による平角材表面きず検査

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Eddy-current testing(ECT) is widely used for detecting surface flaws in steel bars, rods and tubes. However, general methods of ECT(e.g. rotating probe heads) are not applicable to inspection of steel plates because of its rectangular section. Electronic scanning ECT has been studied and developed in order to carry out automated examination of plate surfaces. This is available for non-round shapes and large surface areas. This has multi-coils printed on flexible circuit boards in the face of steel surfaces, and sweeps coils electrically. Consequently this allows inspections for all areas by arranging probes for surfaces and sides of plates. Coil patterns have two typical characteristics as follows: (1) Coils are arrayed for three lines. The second line is shifted 1/3 of a coil width as compared to the first, and the third is shifted 2/3 to the first. This is because sensitivity distributions of the three lines are complement each of the other to prevent from missing detection. (2) With a view to detecting flaws of any direction, each differential coil of the first line is placed at 45° with the line. And each of the second is placed at 135°. These diagonal differential coils provide non-directional detection. Signal analysis is through two digital filter techniques, low-pass filter(LPF) and band-pass filter(BPF). This processing makes it possible to detect flaws whether long or short. Examinations of this scanning ECT show that any kind of defects deeper than 0.5mm are mostly detected for all areas of steel plates.
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電子走査形渦流探傷法による平角材表面きず検査

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