Abstract: The paper addresses the hydraulic characteristics of a heated heavy crude pipeline.It is worth notice that the pipeline does not behave like the usual hot oil pipelines in two ways.Firstly, under given heating temperature and pressure drop, the convergence of the trial—and—error process to solve the flow—rate of the pipeline segment would be likely damaged by an unstable flow-rate interval, in which the friction loss of a pipeline segment decreases with the increase of flow-rate, just contrary to usual oil pipelines.Secondly, the flow of heated heavy crude through the pipeline is probably in the critical regime between laminar flow and turbulent flow.Because of different friction factors of the critical Reynolds number 2000 used as the interface of these two regimes determined respectively from laminar flow and turbulent flow, it is possible that an exact flow—rate can not be found corresponding to the combination of heating temperature and pressure drop of the segment.For the pipe segment, based on its hydraulic calculations at different upstream oil temperatures, different heat transfer conditions between it and its surroundings, and different flow。rates.the curyes of fiction lOSS versus flow-rate are plotted, from which the unstable flow-rate intervals may be determined.From the angle of safe operation, the unstable flow—rate interval should be avoided.