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 inspection apparatus for the inner surface of a pipe comprising: a wheeled carriage adapted to travel along a rail; a supporting rod having a tip portion and secured to the wheeled carriage and adapted to have its tip portion inserted into a pipe to be inspected, said supporting rod being hollow at least in the tip portion thereof and being formed in the tip portion with a window which faces the inner surface of said pipe; a detecting mechanism portion including; a mount housed in the tip portion of said supporting rod and movable radially thereof; at least two detecting portions placed on said mount in parallel to the axis of said supporting rod and having magnetic-sensitive elements which face the inner surface of said pipe to be inspected through said window in said supporting rod; inclined surfaces provided on the under-surface of said mount which support thereon said detecting portions and extending axially of said supporting rod, said inclined surfaces being adapted to engage rollers movable axially of said supporting rod; and two or more guide rollers mounted on said mount in parallel to each other and adapted to roll on the inner surface of said pipe to be inspected, to thereby support said mount, when said magnetic-sensitive elements are brought closer to the inner surface of said pipe to be inspected; a guide mechanism portion including; a supporting frame secured to the tip portion of said supporting rod and adapted to expand in a direction opposite to the direction in which said magnetic-sensitive elements project; and guide rollers attached to said supporting frame and rolling on the inner surface of said pipe, thereby supporting said supporting rod when said supporting frame in expanded; an exciting mechanism portion including; a DC exciting head mounted on the wheeled carriage and adapted to be brought close to the outer surface of said pipe to be inspected and to be moved away therefrom, together with said wheeled carriage, said exciting head including exciting magnets placed in opposed relation to said magnetic-sensitive elements through the medium of the wall of the pipe, and follower rollers suspending said exciting magnets and rolling on the outer surface of said pipe to be inspected, thereby supporting said exciting magnets in the vicinity of the outer surface of said pipe, respectively; and means for rotating the pipe to be inspected about the central axis thereof.