| 摘要 |
PROBLEM TO BE SOLVED: To compress the difference between the estimated value and the actual dimensions and to improve the measuring accuracy by performing the fault detection of an actual pipe at the frequency different from the fault-detecting frequency when the defect of a reference tube is detected. SOLUTION: A fault detecting probe 8 is inserted into a reference tube 9, to which an artificial defect 91 is applied. The fault detecting frequency of the oscillator of a remote-field eddy-current detector 7 is changed, and a fault detecting frequency f2 , where the phaseθof the signal (unbalanced signal) obtained from the part without an artificial fault 91 is obtained. Then, a plurality of the artificial faults, whose depths are different at the fault detecting frequencies f2 , are detected. The phase angleθof the fault signal is obtained. The depth estimating curve (depth versas phase curve) is formed. When the fault of the actual tube 10 is detected, a fault-detecting frequency f3 where the unbalanced signal obtained at the part without the fault of the actual tube 10 is obtained. The fault detection is performed at this frequency f3 . Then, the phase angleθof the detected fault signal is compared with a predetermined estimated depth curve, and the depth of the fault is estimated.
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