MEASURING METHOD OF THICKNESS OF LINER LAYER AND THICKNESS OF ZIRCALLOY OF LINER COATED PIPE

摘要

PURPOSE:To improve measuring accuracy, by applying three frequencies to a coil in a pipe, so that the penetrating depth of one frequency is approximately equal to the total thickness of the pipe, that of one frequency is approximately equal to the thickness of a liner layer and that of one frequency is smaller than the thickness of the liner layer, and removing the fluctuation of lift-off and the change in sensitivity from the measured values of said three signals obtained by said application of the three frequencies. CONSTITUTION:A liner coated pipe (a) comprises a base material of zircalloy and a liner layer of pure zirconium. The pipe (a) is rotated by a rotary machine (b). A probe (d) is moved in the axial direction of the pipe by a driving device (c). A frequency is applied to a coil so that the penetrating depth is approximately equal to the total thickness of the pipe (a). A frequency is applied so that the depth is approximately equal to the thickness of the liner layer. A frequency is applied so that the depth is smaller than the thickness of the liner layer. The change in impedance of the coil is converted into voltage change by an eddy current flaw detector (e). The voltage is inputted to an operating device (f). The effects of the lift-off signal and the sensitivity change to the thickness signals are removed by the operating process based on various relationships of the measured values of the specified 3 frequencies. The thickness of the liner layer, the thickness of zircalloy and the total thickness obtained in this way are displayed on a display device (g).