Automatic Magnetic Flux Leakage Testing Method And System For Sucker Rod Defect Detection

Sucker rod is the essential function part between oil pumping unit and deep well, it longendures the power transmission alternating stress, and meanwhile, combined with theerosion by various kinds of corrosive medium in the environment. It is easily for in-servicesucker rod to generate crack, etching pit, wear, which reduces the strength of the sucker rodand even causes oil drilling accidents when it becomes severe. In order to improve oldsucker rod cycle utilization, a new process for the old sucker rod remanufacturing is widelyused, with which a higher precision nondestructive testing is needed.On the basis of the structure and complicated defects of the rod body, a detectionmethod based on the sucker rod linear moving and double DC coil axial magnetization isproposed. Then, the overall plan of the detection is designed and the difficulties of thedetection are analysed. A procedure for full characterization of the surface-breaking cracksbased on measurements of only one tangential component of the magnetic field with MFLtechnique is proposed, ANSYS simulation and experiment are used to evaluate thedimensions of the defect. To evaluate the length of the defect, signals from several paths areextracted, and the amplitude of the signals are plotted along the defect length, the position ofthe peaks in this derivative gives a proper approximation of the start and end points of thecrack; And, the same method is applied to the width estimation, but signals from only onepath is extracted; In order to estimate the crack depth directly, a calibration surface thatdescribes the maximum of the MFL response with respect to the length and depth of thecrack. An automatic non-destructive testing device is designed aims at the small radius bigcurvature property and the actual detection requirements of the in-service sucker rod, whichincludes the defection host (testing probe, follow-up probe tracking mechanism, thecentering clamp mechanism, magnetizer, demagnetizer), delivery mechanism, on (under)institution and detect motion control, signal conditioning circuit and signal acquisition unit.Field test results show that the automatic MFL testing system for sucker rod designed bythis paper can detect the smallest artificial defects announced by SY/T5643-2010and theconsistency of the signal is better than that of the standard GB/T12606-1999requirement.