Abstract: The premium threaded connections (PTCs) of tubing used in high temperature and high-pressure deep wells are subjected to complex cyclic loads including axial tension-compression cyclic load and radial internal-external cyclic pressure. Under the co-action of complex loads, local elasto-plastic deformation is easy to occur in the connection part, resulting in the increasing risks of leakage, accident, waste and environmental pollution. Therefore, it is crucial to reveal the influence of complex cyclic loads on the deformation of PTCs in the field of oil and gas well engineering. However, the material, martensitic stainless steel, exhibits obvious tension-compression asymmetry and Bauschinger effect under the complex cyclic loads. To account for this, a new model containing the Reduced Cazacu-Barlat J2-J3 yield criterion considering tension-compression asymmetry and the Armstrong-Frederick (A-F) kinematic hardening model considering Bauschinger effect was established. The deformation of PTCs under complex cyclic loads was analyzed, and the results show that the radial internal pressure is the main factor that causes the high contact stress peaks and the accumulation of plastic deformation in the PTCs. The Bauschinger effect caused by the cyclic internal pressure has a large impact on the deformation of the PTCs. Under the axial tension-compression cyclic loads, the plastic deformation only occurs in local threaded connections, so that the Bauschinger effect has no obvious effect on the deformation of the PTCs. The Bauschinger effect affects the deformation of the PTCs much only in early few cycles, but the decrease of the seal contact strength caused by the Bauschinger effect does not significantly, which meets the requirements of sealing integrity of PTCs.

Key words: Bauschinger effect, kinematic hardening, cycle loading, premium threaded connections(PTCs)