| 摘要 |
PURPOSE:To enable the detection of the presence of exfoliation of a coating layer in a non-destructive, in an easy and reliable manner, by making an ultrasonic wave incident on the surface of a steel material with thick anticorrosive coating and by comparing an echo from the bottom of the steel material with a threshold value set in a prescribed manner. CONSTITUTION:A threshold value SL is set in accordance with an attenuation amount to which the condition of the boundary between a coating layer 2 of polyethylene or the like of a steel material 1 with thick anticorrosive coating and the steel material 1 is added, an echo obtained from an ultrasonic wave emitted into the material from an ultrasonic wave transmission-reception device 3 and received thereby is compared with the threshold value, and the result of comparison is displayed. The ultrasonic wave is not propagated when an exfoliated part 4 is vacuum, while the part shows high impedance when there is air in the part. When the exfoliated part 4 exists, an echo P3 to be obtained from the bottom of the steel material 1 in succession to a transmission wave P0, an echo P1 from the surface of the layer 2 and an echo P2 from the interface of the layer 2 with the steel material 1 does not appear. The presence of exfoliation of the coating layer is detected in a non-destructive, easy and reliable manner from the presence of said echo P3. |
