An approximate two-dimensional theoretical model based on a quasi-steady approach is presented for thermal analysis of phase-change processes around an insulated pipeline buried horizontally in semi-infinite frozen soil. The model is verified by comparison with numerical and other approximate solutions from the literature. The theoretical results of this study show that, under constant boundary conditions, the propagation of the thawing/freezing interface is limited. The reverse process occurring as a result of interruption of the fluid flow is also examined. Based on the solution for prediction of the boundary location of thee thawing region, an analytical equation for determination of the fluid temperature as a function of time is developed.