Flaw detector for pipe employing magnets located outside the pipe and detector mounted inside and movable along the pipe with the magnets

Claim 1

A magnetic flaw detector for inspecting inner wall surfaces of a pipe of magnetizable material, comprising: a support rod mounted on a wheeled carriage which is movable along a rail, said support rod having a hollow space at least in the fore end portion thereof to be inserted into said pipe and a window formed in said fore end portion to open toward an inspecting spot on the inner wall surface of said pipe; a detector assembly having a base plate accommodated within said hollow space at the fore end of said support rod and movable radially of said support rod, a plural number of detecting members mounted on said base plate in alignment in the longitudinal direction of said support rod, each one of said detecting members having magneto-sensitive element urged by respective biasing means to project independently through said window toward the inner wall surface of said pipe, and a plural number of guide rollers mounted on said base plate and adapted to be brought into rolling contact with the inner wall surface of said pipe to support said base plate when said detecting members are abutted against the inner wall surface of said pipe; a guide mechanism having a support frame attached to the distal end of said support rod and swingable in a direction opposite to the projecting direction of said magneto-sensitive elements, and a guide roller adapted to be brought into rolling contact with the inner wall surface of said pipe to support said support rod when said support frame is swung out; a magnetizing assembly having a magnetizing head reciprocably mounted toward and away from the outer surface of said pipe, on a wheeled carriage movable with the first-mentioned wheeled carriage to move said magnetizing head longitudinally along the outer wall surface of said pipe, exciting magnets mounted on said magnetizing head in a position closely opposing said magneto-sensitive elements across the wall of said pipe, and follower rollers adapted to be brought into rolling contact with the outer wall surface of said pipe to support said exciting magnets in an operating position close to the outer wall surface of said pipe; and means for rotating said pipe about the axis thereof during the flaw detecting operation by said detecting and magnetizing assemblies.