Stress analysis and concentration coefficient of drill pipe joints based on 3D finite element simulation

Abstract:

In drilling engineering， failures at the threaded connections of drill pipe joints account for up to 86%， making them the primary risk area for drill string failure. To conduct an in-depth analysis of joint stress distribution and concentration characteristics， this study， based on 3D finite element simulation， performed a comparative analysis of the stress in API standard single-shoulder and double-shoulder drill string joints under axial and torsional loads. Furthermore， the axial and torsional stress concentration coefficients for the NC50-type joint were calculated. The findings indicate that： the maximum stress in single-shoulder threads is concentrated at the root of the first thread in the thread engagement area； the maximum axial and shear stresses in double-shoulder threads are significantly lower than those in single-shoulder threads， with reductions of approximately 24% and 27.3%， respectively， exhibiting a more pronounced performance advantage， especially under high torque； the axial stress concentration coefficient for the NC50 joint is 4.21， and the torsional stress concentration coefficient is 3.73. The outcomes of this research provide a significant basis for the performance optimization design of drill pipe joints， precise stress calculation of the drilling system， and fatigue life prediction.