## 1 Introduction  
Steel pipes are widely used in machinery and the marine industry, among other fields [1; 2; 3; 4]. They are subjected to internal pressure and a large cyclic bending load, which may incur a ratcheting effect [5]. The ratcheting effect leads to additional plastic damage [6] and has a great influence on the fatigue performance of the structure [7]. Additionally, ratcheting deformation may not cease until final fracture occurs [8]. Similar to fatigue, creep and other damage mechanisms, the ratcheting effect has been taken into account by many criteria, including RCC-MR [9] and ASME Code Section III [10], for assessing the safety and life prediction of the structure [11].  
In recent years, many researchers have studied the ratcheting behavior of pipes by experimental and numerical simulation. [PERSON] et al. [12; 13; 14] studied the ratcheting behavior of elbow and straight pipes under internal pressure and cyclic loading by experimental and numerical simulation. In their study, several cyclic plasticity models were considered in the ratcheting simulation, including bilinear (BKH) [15], multilinear (MKIN/KINH) [16; 17], Chaboche (CH3) [18; 19], modified Chaboche (CH4) [20], Ohno-Wang [21; 22], modified Ohno-Wang [23; 24; 25; 26], and Abdel Karim-Ohno [27]. They also investigated and analyzed the effect of local wall thinning on the ratcheting behavior. [PERSON] et al. [3] evaluated the thermal effects on the ratcheting behavior of a pressurel elbow pipe using the Chen-Jiao-Kim (CJK) kinematic hardening model as a user subroutine of ANSYS. In addition, they adopted more accurate Chen-Jiao-Kim model parameters to explore the ratcheting behavior of a pressurized elbow pipe under two sets of complex loading paths [28]. The fatigue-ratcheting behavior of thin-walled carbon steel elbow and tee joint pipes were evaluated under internal pressure and seismic loading through experimental and numerical analysis by [PERSON] et al. [29]. Numerical models with a nonlinear isotropic/kinematic hardening model were adopted to evaluate the effects of some key factors--such as the mean stress, loading regime, and material hardening properties--on the ratcheting response of a steel tube with a rectangular defect by [PERSON] and [PERSON] [30]. Finally, [PERSON] et al. [31] studied the ratcheting behavior of a 90\({}^{\circ}\) single unreinforced mitered pipe subjected to a cyclic in-plane closing moment with a non-zero mean value and constant internal pressure by means of experimental and numerical simulation.  
Most of the existing research focuses on the ratcheting behavior of a single pipe. However, the ratcheting response of a pressurized pipe with assembly parts has been not yet been considered and studied. Additionally, in practice, the region near the assembly contact area between the sleeve and the pipe is the most dangerous location, so it is worth examining the ratcheting response of a pipe with assembly parts in that region, as this may lay the foundations for further study on the effect of the ratcheting response on the failure of a pipe. In this work, due to the difficulty of an experimental measurement in the assembly contact area, the ratcheting response of a pipe was studied using an elastic-plastic finite element method with a nonlinear isotropic/kinematic hardening model. Then, the ratcheting responses of pipes with and without assembly parts were compared and analyzed. In addition, the effect of assembly contact between the sleeve and the pipe on the ratcheting response was investigated and is discussed herein. Lastly, the influence of the clearance between the sleeve and pipe on the ratcheting response was also analyzed.