Thermo-mechanical stability analysis of thermosyphons for pipeline soil and their optimal layout in permafrost regions

Abstract

In permafrost regions, warm-oil buried pipelines release vast amounts of heat energy to surrounding soils and lead to rapid permafrost degradation. Settlement disasters induced by permafrost degradation significantly increase the probability of pipeline failure. The two-phase closed thermosyphon (TPCT) can cool soil, inhibiting permafrost degradation, but its deployment is still at the experimental stages along the China–Russia Crude Oil Pipeline (CRCOP). Therefore, it is important to determine an optimal layout for TPCTs that can achieve both effective cooling and cost control. In this study, a strategy for a nonlinear thermo-mechanical coupled model is proposed through Python–Abaqus secondary development. Based on it, the thermal and mechanical effects of TPCTs under different spacings, as well as their optimal layout, are numerically investigated. Closer TPCT spacing leads to a lower degradation rate of frozen soil and a lower peak TPCT heat flux. In addition, the peak pipeline von Mises stress in the transition zone increases for greater TPCT axial distances over time. When the TPCT axial distance is ≤8 m, the minimum pipeline principal strains remain below the critical compression strain over 50 years. Finally, a backpropagation neural network is constructed to predict the maximum pipeline compressive strain, and most prediction results fall within the 95% confidence interval.