An Automation Toolbox for Nonlinear FEA of Rotary Shouldered Threaded Connections

Abstract A rotary shouldered threaded connection consists of a pin element and a box element and acts as a key component to screw together the tools and subs used on the BHA (bottom hole assembly). Functionally, the rotary shouldered connection upon makeup must separate internal and annular pressures, transmit torque, and withstand fatigue loads when drilling through many revolutions in a curved well section. If these connections fail during drilling operation, a twist-off could occur, which could possibly lead to loss of the bottom BHA section in the hole with a tremendous amount of nonproductive time. Finite element analysis (FEA) can be used to capture the nonlinear interactions between the threads and between the seal faces of the pin and box subjected to a tightening torque and service loads such as axial and bending loads. To expedite and standardize such a simulation process, in this paper, a CAE automation toolbox has been developed for standardizing and accelerating nonlinear finite element analysis of rotary shouldered threaded connections. Such a toolbox can automatically create the CAD geometry of the threaded connection that contains tens of design parameters per the standard drawings, assignment of material properties with elasto-plastic models, generation of a desired mesh with refinement in the areas of interest, definition of appropriate contact interactions, application of loading and boundary conditions, and postprocessing of stress and strain results for visualization. The analysis results obtained from the developed automation toolbox were validated by comparing to those obtained manually with a commercially available finite element code (Abaqus). Excellent agreement was observed. The use of the automation toolbox can help shorten the analysis effort from days to only a few hours for nonlinear finite element analysis of rotary shouldered threaded connections. The automation toolbox has been widely utilized to accelerate design iterations of advanced rotary shouldered connections for enhancing drilling performance and reducing maintenance cost for drill stem components as well as root cause analysis of threaded connection failures.