Magnetic inspection device for elongated objects and inspection method

A magnetic inspection device for nondestructively testing elongated objects comprising:

• a first section defining a pole piece and including a magnet for inducing a magnetic field in an elongated object at a first longitudinal station along the object;
• a second section defining a pole piece and including a magnet for inducing a magnetic field in the elongated object at a second longitudinal station displaced along the object from the first station;
• the magnets in the first and second sections being positioned and poled to generate magnetic fields which establish a magnetic circuit extending from one section to the other through the elongated object;
• a third section interposed between the first and second sections, and containing a magnetic flux detector for detecting magnetic flux in the magnetic circuit established by the magnets;
• a ferromagnetic yoke extending between the first and second sections and defining a flux path completing the magnetic circuit externally of the elongated objects;
• and
• mechanical separating means coupled with flux carrying portions of the yoke and at least one of the first and second sections in the magnetic circuit for parting the flux carrying portions from an otherwise assembled condition in opposition to the magnetic attraction forces and interrupting the magnetic circuit to disassemble the inspection device.

A magnetic inspection device for testing elongated objects comprising:

• a first pole piece having a magnet for inducing magnetic flux in an elongated object at one station;
• a second pole piece having a magnet for inducing flux in an elongated object at a second station,
• the first and second pole pieces being of opposite magnetic polarity whereby the induced magnetic flux extends through the elongated object between the first and second stations;
• means for holding the first and second pole pieces in spaced relationship at the first and second stations;
• a yoke extending between the first and second pole pieces and providing a flux return path for completing the magnetic circuit between the first and second pole pieces;
• and
• magnetic flux detector means movable back and forth between the first and second pole pieces for detecting flux changes in the elongated object between the first and second stations.

A method for magnetically inspecting elongated objects by inducing magnetic flux in the object through a first pole piece at one station along the object and a second pole piece at a second station along the object, the two pole pieces being magnetically interconnected by means of a yoke whereby a forward flux path is established through the elongated object between the first and second stations and a return flux path is established through the yoke, and detecting the changes in flux by means of a flux detector positioned between the first and second pole pieces, the method comprising:

• dividing the pole pieces and magnetic flux detector into separate sections;
• positioning the separate sections along an elongated object in spaced relationship;
• moving the sections relative to one another along the elongated object in order to assemble the sections for a test;
• conducting a test with the assembled sections;
• and
• disassembling the sections by separating the sections and positioning them at longitudinally spaced stations along the elongated object and then
• removing the sections individually from the elongated object.