Study on pipeline structural integrity and wear mechanism during horizontal directional drilling pullback of submarine pipelines

Submarine pipelines experience complex multiaxial loads during horizontal directional drilling (HDD) pullback, and their structural integrity and weight coating directly affect engineering safety and service life. This study establishes a nonlinear buckling model with initial geometric defects to investigate buckling mode evolution and post-buckling behavior of large-diameter thin-walled pipelines under complex loading. Based on Donnell–Mushtari–Vlasov shell theory, a method is developed to determine the critical buckling state, and the complete equilibrium path is traced using eigenvalue analysis and the arc-length method, revealing the significant effect of initial defects on buckling load. An innovative multi-scale wear framework for weight coatings, spanning from atomic to macro scales, is also proposed. This study combines molecular dynamics, fractal contact theory, and fracture mechanics to analyze energy dissipation and material transfer during wear. Full-scale field and laboratory tests verify the model accuracy, and a multi-mechanism coupled wear prediction model based on the Archard formula is established. The key quantitative findings of this study are as follows: (1) initial geometric imperfections reduce the buckling load by 15% to 30% and diminish the post-buckling reserve capacity by 40%–60%; (2) under drilling mud lubrication, the wear rate decreases by 70%–85%, and the wear depth follows a power-law relationship with contact stress; (3) the pipeline strength reliability index β equals 3.52 under normal pullback conditions, corresponding to a failure probability of 2.18 × 10−4, which satisfies the DNV-OS-F101 target for the ultimate limit state; (4) the optimal ranges of key construction parameters are a pullback speed of 0.8–1.2 m/min, a mud viscosity of 45 to 60 mPa·s, and a burial depth of 2.0–3.0 times the pipeline diameter.