Research On Quantitative Detection Of Surface Cracks On Pipe String Based On Circumferential Electromagnetic Field Measurement Technology

According to the requirements of cracks detection on pipe string in oil & gas industry,a circumferential electromagnetic field measurement(CEFM)method and system are present refering to the principle of ACFM technology to achieve exhaustive,rapid and quantitative detection of cracks on pipe string using a coaxial excitation coils which afford a 360°broad circumferential excitation area.By theoretical analysis,numerical modeling and experiments,the theoretical model of CEFM is built.The distorted electromagnetic field is analyzed around the crack on the surface of pipe string.The inversion algorithm of crack size is proposed.The CEFM test system is set up and the crack quantitative detection experiments are carried out.The main works are summarized as follows:(1)Theoretical and numerical simulation models of CEFMAccording to the theory of classical electromagnetism,the theoretical model of CEFM is present based on ACFM using a coaxial excitation coils which afford a 360° broad circumferential excitation area.The finite element method(FEM)is employed to build the numerical simulation model of CEFM and analyze the distorted electromagnetic field around the crack on the surface of pipe string.The characteristic signals of crack are extracted by simulation model.The theoretical and numerical simulation models lay the foundation for the parameters optimization and characteristic signals analysis.(2)Parameters optimization and crack quantification analysisBased on the model of CEFM,the parameters(such as excitation,lift-off)are optimized,which provides the basis for the design of CEFM system.The distorted region of electromagnetic field around the crack is analyzed by simulation and experiments,which determines the space of detection sensor array.The relationship between characteristic signals and crack size is analyzed and the crack quantification algorithm is proposed.(3)CEFM system development and crack quantative detection experimentsAccording to the optimized results by simulation model,the probe,sensor array and hardware of CEFM are designed and the intelligent identification software is developed.A CEFM system is set up integrated with probe,signal processing hardware and intelligentsoftware.The crack test experimens are carried out using CEFM system.The rsults show that the CEFM system can detect all the surface cracks exhaustively,rapidly and quantificationally on pipe string in one pass scanning.