| 摘要 |
PURPOSE:To detect a defect exactly, by constituting so that the shape and arrangement of a transmitting coil and a receiving coil satisfy prescribed conditions. CONSTITUTION:Transmitting and receiving coils 13, 14 are placed symmetrically along the inside face of a tubing 4, on the end face of supporting parts 12a, 12b of a permanent magnet 11 having an end face curvature running along the inside face of the tubing 4 being a body to be inspected, and length LT of the transmitting coil and length LR of the receiving coil satisfy the following equation. LR=T0(n+1/2)+LT (n=0, + or -1, + or -2,...). When a high frequency current is made to flow to the transmitting coil 13, an eddy current I is generated on the wall face of the tubing 4 being in the vicinity of the oil 13. On the other hand, a magnetic flux B of the circumferential direction is applied to the wall face of the tubing 4 by the magnet 11, and a transversal wave whose wavelength is equal to T0 is generated by a mutual action with I. In ultrasonic waves generated in the tubing 4, as for clockwise and counterclockwise transversal waves which reach the receiving coil, the phase is shifted by 1/2 and is offset, and only a defect signal is fetched, therefore, a defect is detected exactly. |
