In magnetic-particle testing, the maximum leakage flux from a flaw is obtained when the direction of the magnetic flux is normal to the longitudinal direction of the flaw. Since we usually cannot predict the direction of the flaw to be detected, it is necessary to perform the testing at least two times by changing the direction of magnetization. In a rotating field type magnetizer using a three-phase alternating current (AC), any directional flaw can be detected by a single testing. However, until now, the details of the rotating magnetic flux density in a specimen and its change with time have not been understood. In this research, the distributions of the rotating magnetic flux density were evaluated by measuring this density in three directions using Hall elements and by numerical analysis. The distributions of the magnetic flux density around the flaw were also evaluated by numerical analysis. The distribution of the rotating magnetic flux density near the central part of the magnetizer was made clear, and it was confirmed that the distribution became more uniform by equalizing the impedance of each coil of the magnetizer.

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