Apparatus for inspection of tubular ferromagnetic members using plural movable search shoes for identifying area depth and location of discontinuities

Claim 1

IN A MULTI-PURPOSE APPARATUS FOR NON-DESTRUCTIVE INSPECTION OF OIL WELL PRODUCTION TUBING TO ACCOMPLISH (1) DETECTION AND MEASUREMENT OF THE DEPTH OF ROD WEAR AND (2) DETECTION OF LONGITUDINAL SEAMS AND LIKE DISCONTINUITIES, THE COMBINATION OF AN ASSEMBLY CONSTRUCTED TO SURROUND THE TUBING TO BE INSPECTED, SAID ASSEMBLY COMPRISING MAGNETIC MEANS FOR ESTABLISHING A MAGNETIC FIELD EXTENDING TRANSVERSELY THROUGH THE WALL OF THE TUBING, ROD WEAR CAUSING RELATIVELY BROAD AREAS OF LEAKAGE FLUX TO APPEAR AT THE OUTER SURFACE OF THE TUBING, SEAMS AND LIKE DISCONTINUITIES CAUSING RELATIVELY NARROW AREAS OF LEAKAGE FLUX TO APPEAR AT THE OUTER SURFACE OF THE TUBING, SAID BROAD AND NARROW AREAS SUBTENDING APPROXIMATELY THE SAME ANGLES SUBTENDED BY SAID ROD WEAR AND SAID SEAMS AND LIKE DISCONTINUITIES, SAID ASSEMBLY FURTHER COMPRISING A PAIR OF SEARCH SHOES EACH CARRYING A ROD WEAR SEARCH COIL AND A SEAM SEARCH COIL, SAID SHOES BEING MOUNTED ON SAID ASSEMBLY IN SUCH FASHION AS TO BE DISPOSED IN OPPOSITION TRANSVERSELY ACROSS THE TUBING WHEN SAID ASSEMBLY SURROUNDS THE TUBING; A FIRST ELECTRICAL CIRCUIT INCLUDING SAID RODNDS THE TUBING; A FIRST ELECTRICAL CIRCUIT INCLUDING SAID CAL INTEGRATING MEANS OPERATIVE TO CONVERT SIGNALS INDUCED IN SAID ROD WEAR SEARCH COILS, BY PASSAGE THROUGH SUCH BROAD AREAS OF LEAKAGE FLUX, INTO OUTPUT SIGNALS INDICATIVE OF TOTAL FLUX RATHER THAN RATE OF CHANGE OF FLUX, SAID INTEGRATING MEANS HAVING A TIME CONSTANT AT LEAST SUFFICIENTLY LONG TO EQUAL THE TIME OF SAID PASSAGE; A SECOND ELECTRICAL CIRCUIT INCLUDING SAID SEAM SEARCH COILS, AND SECOND ELECTRICAL CIRCUIT BEING OPERATIVE TO PROVIDE OUTPUT SIGNALS IN RESPONSE TO SIGNALS INDUCED IN SAID SEAM SEARCH COILS BY PASSAGE THROUGH SUCH NARROW AREAS OF LEAKAGE FLUX; ELECTRO-RESPONSIVE MEANS CONNECTED TO SAID CIRCUITS TO RESPOND TO SAID OUTPUT SIGNALS, AND MEANS FO EFFECTING RELATIVE ROTATION, BETWEEN SAID ASSEMBLY AND THE TUBING, ABOUT THE AXIS OF THE TUBING.