| Drill pipes are widely used in the exploration process of the petroleum and natural gas industry.The threads at the ends of the drill pipes are used to connect the drill pipes to each other and bear the working load of the drill pipes during operation.However,fatigue fracture,corrosion,and wear of the drill pipe connection threads can occur after long-term use,which can lead to connection failure and major safety accidents during service.Therefore,defect detection of drill pipe threads is of practical significance.Defects at the root of the drill pipe threads are often covered with oil pollution,making it difficult to visually inspect them,and can easily cause thread fracture failure,posing a significant safety hazard.In response to the current situation in which there is limited research pertaining to the expeditious detection of drill pipe thread root defects in China,this paper conducted research on electromagnetic detection technology for thread root defects.First,the principles of two electromagnetic detection methods,magnetic field interference detection and differential eddy current detection,were studied.The process of the study elucidated the interplay between the magnetic field generated by magnetic field excitation and the tested material,while illustrating the impact of defects on the spatial distribution of the magnetic field within the tested component via magnetic field distribution maps.The use of a dual magnetic circuit structure was proposed to achieve more pronounced defect detection signals.The spatial variation of the analysis of the magnetic field was conducted,establishing a correlation between the variation in magnetic field strength and the resultant output voltage of the Hall element.The principle of differential eddy current detection was analyzed,and the phenomenon of eddy currents in electromagnetic induction was described.By analyzing the impedance of the eddy current coil,the relationship between defects and coil impedance was deduced.The use of differential eddy current methods was proposed to reduce interference factors in detection,and the relationship between defects and the voltage at both ends of the AC bridge was derived.Then,finite element analysis was conducted on magnetic field interference detection and differential eddy current detection.A simulation model for detecting magnetic field interference was established using finite element analysis software,and defect detection simulation experiments were conducted on drill pipe thread root defects.The process of changes in magnetic field distribution caused by defects in magnetic field interference detection was analyzed,and the dual magnetic circuit structure was found to be more effective in defect detection signals than the single magnetic circuit structure.The signal characteristics of defect detection under different defect types were explored.A simulation model for the detection of differential eddy currents was developed,and it involved analyzing the distribution of eddy currents on the specimen’s surface as well as the dynamics of voltage changes at both ends of the AC bridge.The signal characteristics of defect detection under different defect types were explored.Finally,a laboratory test platform for magnetic field interference detection and differential eddy current detection was constructed,and detection experiments were conducted on threads with defects.The experimental findings demonstrated the efficacy of both magnetic field interference detection and differential eddy current detection in effectively identifying drill pipe thread root defects.Moreover,the observed trend in the variation of defect signals during detection was consistent with the results obtained from simulation analysis.Magnetic field interference detection has a better signal-to-noise ratio compared to differential eddy current detection.Based on magnetic field interference detection methods,a drill pipe thread root defect detection device was developed and used to detect defects in drill pipe threads. |
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