Research On The Magnetic Flux Leakage Inspection Of Thread Based On Finite-Element Analysis

End effect and inspection blind area exist in the inspection of Rod and Pipe end by traditional MFL inspection method, so a new method must be researched to inspect those special area. ANSYS, which is a very prevalent finite element analysis(FEA) software, is used to calculate and simulate the coil magnetization and magnetic circuit design , new magnetizing method and magnetic inducing method which can reduce the limitation of traditional MFL inspection method. In the paper, a method of thread inspection and the primary test result was given.Firstly, the basic theory of MFL and the basic structure of MFL inspection are introduced. The establishment of Mathematic module and the analysis of load and boundary conditions based on the theory of finite element analysis and electromagnetic are indicated. The software kit of Emag in ANSYS is selected as the analysis tool.Secondly, the process of model establishment and analyzing of the 2D finite element model are narrated and the analysis result is given. After analysis and calculation,the size and characteristics of MFL type signal have been got.Validity of the model are validated by the experimental data.Thirdly, A FEA model to analyze and design the geometrical size of magnetizer of drill pipe threads inspection is introduced. The influence of the geometric size of the magnetizer on pin thread magnetization of drill pipe in magnetic circuit design is analyzed. The result can be used in magnetic circuit design for improving magnetic effect and testing sensitivity and for providing a method for optimizing the magnetization design in MFL inspection probe.Finally, combining FEA with signal processing, a new method to inspect sucker rod thread is introduced, using ferromagnetic auxiliary rod to connect the end of rotating sucker rod and fixed probe to detect the MFL signal.