MAGNETIC-PARTICLE FLAW DETECTOR FOR STEEL PIPE

PURPOSE:To make it possible to detect the defects of the entire surface along the entire length automatically with a compact equipment by aligning a magnetizing/ magnetic-particle spraying device comprising #-shaped twin coils or the like and a rotary imaging device in series along a straightforward line for a steel pipe under inspection. CONSTITUTION:A cylindrical coil 41 is spirally wound along the pipe axis of a steel pipe under inspection 1, and the steel pipe 1 is freely inserted into and removed from the tube part. The coils is excited with a DC power supply. For twin coils 42, three- phase AC power supplies, whose phases are deviated by 120 degrees to each other, are connected between facing rectangular-shaped coils 42a and 42c and 42b and 42d, and the rotating magnetic field is generated. Then, magnetic particle liquid is sprayed from a magnetic-particle-liquid spraying nozzle 45 toward the steel pipe 1. When the steel pipe 1, to which the magnetic particles are attached, is conveyed to the position of a rotary magnetic-particle-pattern imaging device 5 provided on a frame, a rotary body 56 is rotated, and the steel pipe 1 is illuminated with an ultraviolet-ray source 57 arranged at the rotary body 56. The image of the entire surface of the steel pipe 1 along the entire length is picked up with a CCD line sensor 54. The picked-up image signal is sent into an imaging device, and the defect is automatically detected and judged.