To provide a method of inspecting damages and a corrosion thickness reduction phenomenon caused by hydrogen, capable of detecting the damage resulting from the hydrogen in HIC, HA or the like, even when pressure-proof member in equipment/wiring or the like are corroded in various petroleum plants, capable of detecting accurately the damages caused by HIC, HA of a steel material constituting the equipment or the like.

In this inspection method of supplying ultrasonic wave UW to an inspection object I, to detect a defect inside the inspection object I, while changing the convergence position of the ultrasonic wave UW along a thickness direction of ultrasonic wave UW, the convergence position of the ultrasonic wave UW is also moved along the surface of the inspection object I, reflected waves of the ultrasonic wave UW at the inspection object I is detected to form an echo height distribution, indicating the distribution of an echo height of the reflected waves in the inspection object I, based on the total reflected waves detected in the respective convergence positions, and the damage caused by the hydrogen, such as the hydrogen induced cracking and the hydrogen corrosion is discriminated, based on a distribution of defect areas, having a prescribed value or larger for the intensity in the echo height distribution.

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