MFL-Testing Method And Apparatus For Drill Pipes' Upsetting Tapered Belt With Pulsating Magnetization

The drill pipe is affected by many kinds of forces during its service,which is easy to produce cracks,corrosion and other defects,eventually leading to failure and accidents.In particular,the accidents caused by fatigue puncture of thickened belt account for the highest proportion.Therefore,it is essential to strengthen the nondestructive testing of drill pipe thickening belt.A method based on pulse magnetization for MFL(magnetic flux leakage)testing of thickened drill pipe is proposed to solve the problems,such as large volume and heavy mass of magnetizer,difficulty movement in axial of probe on step surface,and poor portability.This method uses flexible static array induction coil to detect the change of AC magnetic field on the surface of the rod,arranges profiling detection probe along the axial step of the thickened belt,and scans the detection section surface along the circumference of the drill pipe,so as to realize the light MFL testing of the thickened belt of the drill pipe.From the three aspects of theory,simulation and experiment,the feasibility of picking up defect leakage magnetic field in drill pipe thickening belt with DC pulsating magnetization is analyzed.In order to eliminate the interference of step magnetic refraction,the influence of the strong and complex background magnetic field is eliminated by the method of mutual difference of detection signals at different circumferential angles.In order to optimize the parameters of magnetizing current,the influence factors of DC pulsating magnetizing flux leakage signal are explored through experiments.Consider above research content and actual engineering requirements comprehensively,pulsating magnetization method is applied to the MFL testing system,and the process and the structure design are completed.Based on the principle of pulsating magnetization,the lightweight design of the magnetizer is realized;At the same time,a magnetizing power supply is designed to match the requirements of pulse magnetization,a method of induction coil of flexible array is put forward,the time-sharing acquisition system is designed to solve the problem of quantity matching and cost between array signal number and channel.The experimental results show that the system can be used to detect the inner wall defects of the thickened drill pipe.The detection system has the advantages of low cost,small size and easy to carry,and has a wide application prospect.