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This study evaluated the applicability of nondestructive microwave testing method for the long-range detection of inner-surface cracks in metallic tubes. Two seamless straight tubes 7 m in length and 23.0 mm in inner diameter were prepared, and arti cial circumferential slits penetrating the tube walls were introduced. A probe to propagate microwave inside the tube, designed based on three-dimensional nite element simulations, was attached to an end of the tube, and the re ections of the microwave propagating inside the tube were measured using a network analyzer. The experiments con rmed clear re ections due to the slits situated 6 m away from the probe. Furthermore, imposing a signal processing method to compensate for the dispersion of the microwave clari ed the re ections and enabled the slit to be localized quantitatively from the time-of-ight of the re ections.

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