Research On The Evolution Of Piezomagnetic Field Of Defective Specimens Of Deep-sea Pipeline Steel Under Cyclic Tensile Loading

Deep-sea pipeline plays an important role in offshore oil and gas resources development.In the process of deep-sea pipeline service,it is inevitable to be affected by external stress,resulting in stress concentration and failure of pipeline steel material.Nondestructive testing technology based on piezomagnetic effect can detect defects and damage of ferromagnetic materials by on-line monitoring the piezomagnetic field signal near ferromagnetic materials.Due to its high sensitivity,it can predict early damage and other advantages,showing great potential.At present,the research of nondestructive testing based on piezo-magnetic effect is mainly focused on off-line metal magnetic memory testing technology,and the research on on-line piezo-magnetic field testing technology is less.Based on the cyclic loading test of ferromagnetic steel with defects,the evolution of compressive magnetic field near the defective specimen with stress is studied and the test results are explained from the microscopic point of view.Firstly,cyclic loading tests of X70 defective specimens were carried out in this paper.By recording the compressive magnetic field signals of the material under cyclic stress in real time and co MParing them with smooth specimens of the same material,the evolution rules of the components of the compressive magnetic field in different directions of the defective specimens were obtained,and the concept of the normal differential magnetic field was proposed.Secondly,this paper studies the influencing factors of normal compression magnetic field of deep-sea pipeline steel defective specimens through axial cyclic loading tests under different conditions.Finally,the variation of compressive magnetic field near the defect of X65 steel under different stresses was obtained through the study of the force-magnetic relationship curve and the characteristic parameters of the curve through the cyclic loading tests with variable valley value and variable amplitude value.By studying the compressive magnetic field of ferromagnetic material defect specimens under different stress states and different external conditions,it is further verified that the method of nondestructive testing of material defect by compressive magnetic signal is feasible.