Abstract: For crude oils with a high solidifying point, freezing can easily occur when the flow is stopped. Determining the maximum stopping time is therefore crucially important for safe rebooting of the system. This stopping time depends on the heat storage capacity of crude oil, heat transfer conditions of the pipeline system and surrounding soil temperature field. This paper reports a numerical study on the unsteady state heat transfer of an oil transportation line under the stopping conditions. The results indicate a strong natural convection in the crude oil and the temperature of crude oil in pipeline drops rapidly in the initial stage of the stopping transportation, and the temperature decrease slows down with time. Such a change in the time dependence of temperature is related to the change of heat transfer mode from natural convection and conduction in the initial stage to conduction in the late stage. For the conditions considered in this work, the oil temperature drops to 38 ℃ after 21 hours, suggesting the stopping time should not exceed 21 hours.

Key words: submarine pipeline, crude oil heat storage, temperature drop, numerical simulation, FLUENT