| 摘要 |
PURPOSE: To obtain a proximate distance of double tubes by using the difference between the maximum magnetic flux leakage value and the minimum magnetic flux leakage value as a parameter, and using the graph of the (proximate distance)/(magnetic flux leakage value) known beforehand. CONSTITUTION: The inner wall of a conduit is sequentially magnetized in the circumferential direction. The value of the magnetic flux leakage at the respective point of the inner wall is measured. Then, the maximum magnetic flux leakage value BH and the minimum magnetic flux leakage value BL are taken out from the magnetic flux leakage values at these measured sites. The differenceΔB between the maximum magnetic flux leakage value BH and the minimum magnetic flux leakage value BL is obtained. Then, based on one of a plurality of the graphs of (the magnetic flux leakage value)/(proximate distance), which have been given beforehand, a central point O on the side of the proximate distance axis (abscissa) is made to be the reference. A pointαand a pointβare set at the positions separated by the equal distance on the right and left sides. The difference between the magnetic flux leakage value at the pointαand the magnetic flux leakage value at the pointβis made to become the differenceΔB between the maximum magnetic flux leakage value BH and the minimum magnetic flux leakage value BL. At this time, the pointαat the position on the left side of the central point O indicates the most proximate distance, and the pointβat the position on the right of the central point O indicates the most remote distance. Thus, the errors in measurements can be suppressed.
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