Eddy current testing method and eddy current testing apparatus

An eddy current testing apparatus having a spinning plate and a probe coil disposed on the spinning plate and located differently from a spinning center of the spinning plate, for detecting a flaw occurring in a columnar or cylindrical subject to be tested by spinning the spinning plate disposed to be opposite to the subject to be tested, relative to the subject to be tested, thereby conducing spinning scanning of the probe coil, wherein

• the probe coil is a probe coil capable of obtaining a differential output about a scanning direction of a detection signal which corresponds to a detected eddy current induced in the subject to be tested,
• the spinning plate is positioned so that a straight line passing the spinning center of the spinning plate crosses with an axial center of the subject to be tested at right angles,
• relative to a test piece made of the same material as that of the subject to be tested, which is provided with an axially extending artificial flaw and a circumferentially extending artificial flaw whose depth is equivalent to depth of the axially extending artificial flaw, a distance between the spinning center of the spinning plate and a center of the probe coil is set so that a difference between a maximum amplitude of a differential output at the axially extending artificial flaw provided in the test piece and a maximum amplitude of a differential output at the circumferentially extending artificial flaw provided in the test piece falls within a predetermined range, and
• spinning scanning of the probe coil is conducted relative to the subject to be tested which is not provided with an artificial flaw by spinning the spinning plate to detect a flaw occurring in the subject to be tested.