| 摘要 |
PURPOSE:To detect accurately defects in the axial direction of a wide-range part of a steel pipe having a proper magnetic field, by arranging a rectangular electromagnet in the steel pipe eccentrically toward one side. CONSTITUTION:An electromagnet 6 is arranged in a steel pipe 1 so that a magnetic pole 6a is parallel with the axial direction of the steel pipe 1 and the electromagnet 6 is deflected to one side from a center axis 11 not to be brought into contact with the inside face of the steel pipe 1. By this arrangement, the inside of the steel pipe 1 is divided to a narrow arc part in one side of the electromagnet 6, namely, a narrow-range part A and a wide arc part in the other side, namely, a wide-range part B. When an AC current is supplied to a coil 7 of the electromagnet 6 to make the narrow-range part A saturated magnetically by a magnetic flux 12 and a proper magnetic field is given to the wide- range part B by a magnetic flux 13, the magnetic powder pattern of a defective part 5 is formed accurately because the fluorescent magnetic powder scattered from a nozzle 10 is scattered in the proper magnetic field. |
