Unsteady heat transfer loop test for buried hot oil pipeline

Through the large-scale buried commercial test loop, the process of the pipeline commissioning preheating and the restart after shutdown were simulated, and the experimental research of buried hot oil pipeline heat transfer law was carried out. The relations between the building of soil temperature field and its recovery time after shutdown and restart were analyzed from the aspects of soil heat storage, isotherm and so on. The research results showed that for the process of the buried pipeline preheating, the shape of the soil isotherm around the pipeline was stable after commissioning 7 days, but the temperature was gradually increased with time increasing; the shape of the soil isotherm around the pipeline was oval after commissioning 10 days, the horizontal radius was 1.2 m, and the vertical radius was 0.9 m; the soil temperature variation was small at a distance of 1.4~2.0 m around the pipeline. During the first 3 hours after restart, the growth rate of the soil heat storage was largest. In order to facilitate the recovery of soil temperature field, the stable oil temperature should be kept, and the variation of working conditions should be minimized as possible within the first 10 hours after restart.