The MFL Testing Method And Instrument For Drill Pipe At Wellhead

Drill pipe is the essential part of the drill string, it endures tension, pressure, torsion,bending and all other kinds of complicated alternating stress, and meanwhile, it also can becorroded by various kinds of mediums during its service process. It is quite easy for drill pipeto generate crack, piercement and wear, which reduces the strength of drill pipe and evencauses drilling accidents when it becomes severe. Detection of defects and scrapping drillpipe in time, can not only reduce the number of drilling accidents, but also prolong the servicelife of drill pipe, which is of great significance to engineering practice. Therefore, this papercarries out the research of the MFL testing method and instrument for dill pipe at wellhead.The structure and the common defects of drill pipe are analysed and the MFL testingmethod based on DC coil magnetization at wellhead is proposed. The overall plan of thedetection is designed according to the actual pull out process, and then the difficulties of thedetection are analysed. The single magnet coil and the space between the double coils aredesigned optimally by ANSYS. The axial and radial component and liftoff characteristics ofdefect’s magnetic flux leakage field are obtained and the radial component is selected as themeasurement standard. The sensor is designed and the array structure is proposed byexperiments, which can increase the peak of the detection signal and guarantee theconsistency of the detection signal. The instrument for dill pipe at wellhead is designed basedon the actual detection requirements, which includes the probe tracking mechanism, magnetcoil and its installation mechanism, signal conditioning circuit and signal acquisition unit.Field test results show that the instrument designed by this paper can detect the smallestartificial defects announced by API Spec5D and the consistency of the detection signal isbetter than that of the standard GB/T12606-1999requirement.