Research On Magnetic Leakage Detection Technology For Gas Storage Well

CNG(compressed natural gas)storage well is a tubular structure that is buried vertically underneath to store compressed natural gas.It is a safe,economical and reliable pressure vessel and has been widely used in CNG gas station because of several advantages such as:large storage capacity,small floor space,safety and stability.Most of the structure is buried in the ground,influenced by the formation corrosive medium and the corrosion factors such as hydrogen sulfide in the storage medium,the pipe wall will be corroded,thinned and even leaked.According to the relevant regulations of SY/T6535-2002,the CNG storage wells in gas station need to be fully non-destructive testing every six years.In order to improve the detection efficiency and reduce the work intensity,the MFL(magnetic flux leakage)detection system for gas storage wells is developed with high efficiency and easy to carry,which can effectively evaluate the safety of gas storage wells and prevent dangerous accidents.According to the principle of MFL and the structural characteristics of gas storage wells,a MFL detection system suitable for gas storage wells of size ?244.48 mm ×11.05 mm has been developed in this paper.Using the finite element analysis software,the MFL analysis model is established.The influence of magnetic spacing and armature cross-sectional area on magnetic leakage field is analyzed.The effects of axial excitation structure and circumferential excitation structure on axial groove defect detection are analyzed.Two different types of excitation structures,axial magnetization and circumferential magnetization,are optimized for the size of the excitation structure based on the results of finite element analysis.The variation law of the leakage magnetic field signals of the inner and outer wall defects and the outer wall defects of different depths is analyzed,and the difference of the leakage magnetic field signals is obtained.The gas storage wells detection device and delivery platform are constructed.Combined with the laboratory OPMS system,preparing artificial simulated defect testing pieces,the comprehensive experimental studies is conducted to research the leakage magnetic field signals of gas storage wells.The results show that the signals of the inner wall defect is stronger than the outer wall defect,and the amplitude of different depth defects is different.The signal amplitude of the leakage magnetic field increases,with the increase of the defect depth.We can judge the severity of the defects based on the MFL signal,this designed system can meet the requirements of on-site detection.The research in this paper is based on the principle of MFL to provide an efficient detection scheme for non-destructive testing of gas storage wells.It provides an important technical guarantee for the safety assessment and risk prevention of CNG storage wells,which is conducive to the effective development of gas wells risk assessment.To ensure the safe operation of gas storage wells.