Study On Strength And Tightness Of Special Threaded Joints Under Complicated Working Conditions

Integrated pipe column of gas well fracturing operation can realized the process of fracturing,completion and gas production in gas well fracturing be completed in a pipe column,reducing the number of pipe columns,but in various processes,the load changes greatly,so the seal of the pipe string is greatly affected.Besides,in the process of fracturing,high viscosity fracturing fluid carries a large amount of sand on the pipe string,which will cause erosion and wear,and the size of erosion wear will directly affect the safety of gas seal and pipe column.This paper selects the special threaded joints as the research objects,based on the structure,dimensions and tolerances of special threaded joints,the geometric model of special threaded joints that is established by using the three coordinate measuring technology.In this paper,a finite element model suitable for strength and sealing of special threaded joints is established by using the finite element analysis software,and the finite element model is verified and corrected through indoor air seal test data.The strength and tightness of special threaded joints under complex loads are studied by using the revised numerical calculation model.The result shows that with the increase of axial tensile load,the contact pressure of sphere-sphere decreases rapidly,and the cylinder-cylinder seal structure remains unchanged.When the internal pressure is combined with the axial tension,the vice-seal surface is a cylindrical-cylinder seal,which restricts the deformation caused by the internal pressure,so the contact pressure of the main seal varies little.In the selection of sealing surface structure,the sealing structure of spherical surface,cylinder-cylinder has respective advantages.The contact pressure and contact area should be taken into overall consideration,and the special thread joint suitable for different working conditions should be selected.With the increase of external pressure,the deformation caused by internal pressure decreases,and the equivalent stress on the tooth and tube caused by internal pressure can be reduced under a certain external pressure,meanwhile,the effect on the sealing is less.Therefore,proper external pressure is helpful to improve the performance of pipe string.Through the combination of experiments and numerical simulation,the influence rules of erosion on the integrated pipe column is studied,and the erosion wear of the tube wall after fracturing is obtained,and two gradients were selected to study the strength and sealing of the special threaded joint.The result shows that the contact state ofthe special thread joint occurs changes in the range of 18.15% of the tube wall erosion,the production and fracture conditions.the drop of contact pressure at the torque shoulder tends to decrease to 0MPa,the contact pressure of the main sealing face and the vice sealing face is newly distributed,and the connection strength of the pipe body is decreasing,with a maximum decrease of 19.6%.The strength and tightness of the threaded joint can still meet the design requirements under the actual load of the studied well after erosion wear.The research methods and results of this paper can be used to analyze the strength and seal of the integrated pipe column,which can provide technical support for the popularization and application of the integrated pipe column of gas well fracturing.