Magnetic testing method and apparatus

A magnetic testing method comprising:

• applying, to a test object, a rotating bias magnetic field which is excited by using an AC current as an exciting current;
• applying, to the test object, a rotating AC magnetic field which is excited by using a superimposed AC current in which a first AC current of the same frequency as that of the AC current that is the exciting current for the rotating bias magnetic field and a second AC current of a frequency higher than that of the first AC current are superimposed as an exciting current and which is 90 degrees out of phase with respect to the rotating bias magnetic field;
• and
• detecting a flaw based on leakage flux produced by the application of the magnetic fields.

A magnetic testing apparatus comprising:

• a first magnetizing device for applying a DC bias magnetic field to a test object in substantially parallel to the direction in which a flaw to be detected extends;
• a second magnetizing device for applying an AC magnetic field to the test object substantially perpendicularly to the direction in which the flaw to be detected extends;
• and
• a detecting device for detecting leakage flux produced by the magnetization of the test object accomplished by the first magnetizing device and the second magnetizing device.

A magnetic testing apparatus comprising:

• a first rotation magnetizing device for applying, to a test object, a rotating bias magnetic field which is excited by using an AC current as an exciting current;
• a second rotation magnetizing device for applying, to the test object, a rotating AC magnetic field which is excited by using an superimposed AC current in which a first AC current of the same frequency as that of the AC current that is the exciting current for the rotating bias magnetic field and a second AC current of a frequency higher than that of the first AC current are superimposed as an exiting current and which is 90 degrees out of phase with respect to the rotating bias magnetic field;
• and
• a detecting device for detecting leakage flux produced by the magnetization of the test object accomplished by the first rotation magnetizing device and the second rotation magnetizing device.