Study On Mechanical Behavior And Magnetization Process Of Oil Well Tubing Joint Thread

Oil well tube is the absolutely necessary material in the petroleum drilling industry,and the whole production work depends on its quality safety.So nondestructive testing should be implemented on new products before being used and old ones during repairing process.Oil well tubing thread is the weakest link,surface injury spondylolisthesis and fracture crack usually occur firstly.P110 tubing joint is selected as the study object and mechanical behavior of meshing thread under the compact status is analyzed based on plastoelasticity.Mechanical behavior of the joint thread surface and distribution law are researched by establishing mathematical model and finite element analysis.It turns to be that the stress distribution of thread teeth is quite uneven,and stress on the several thread teeth of the two ends of the tubing joint is quite large.Invalidation occurs there firstly.Therefore nondestructive testing should be implied mainly on the several thread teeth of the two ends of the tubing joint . Suitable magnetization mode and parameters are selected and magnetic field distribution of P110 tubing joint thread is simulated by using finite element analysis method.Vertical electromagnetic field uniformly distributed along each thread tooth surface is obtained by applying a cushion block with 10 mm depth and a coil 15mm longer than before.Transverse crack on the thread surface can be found out by using this kind of magnetic field.Meanwhile,center conductor magnetization process is simulated and annular magnetic field along thread surface is obtained.Vertical crack on the thread surface can be found out by using this kind of magnetic field.In addition,in order to research defect size parameters effect on leakage magnetic field,crack magnetic charge model on the thread surface and hole type defect magnetic charge model under the thread surface are established based on the magnetic dipole theory.Each defect size parameter effect on leakage magnetic field is analyzed,and it turns to be that when the ratio of depth to width of the crack is large,the leakage magnetic field signal increases when the depth or the width of the crack increases.But also,there exists a range of the defect detection.For hole type defect,the leakage magnetic field signal increases when the size of the defect is bigger or it is nearer to the thread surface,and then,it is easier to be found.And also,there exists a range of the defect detection.As most of the defects on the thread surface are transverse cracks,leakage magnetic field of transverse crack in the bottom of the thread tooth is mainly simulated and cracks with different positions and size parameters are made.The leakage magnetic field of each kind of crack is simulated and it turns to be that under the magnetization current during the simulation only cracks in 0.45 mm range from the bottom of the thread tooth can be found.In addition,the size and shape of the crack have a big effect on the leakage magnetic signals.The bigger the crack is,the easier it is to be found.When the crack with a depth of 0.6 mm is 0.45 mm far from the bottom of the thread tooth it cannot be found when its width is smaller than 0.6 mm.Moreover,when the ratio of depth to width or width to depth of the crack is 1/2 or 1/1,the leakage magnetic field is much more obvious and it is easier to find this kind of crack.