Study on the temperature drop process of the buried hot oil pipeline during shutdown

The insulation layer thermal resistance and the soil characteristics around influence the characteristics of the temperature drop of waxy oil pipeline during shutdown. The temperature drop process of crude in the pipeline is a unsteady heat transfer problem with a moving phase interface while the wax precipitation, the properties of the crude depend on the temperature. The temperature drop process of the buried hot oil pipeline is simulated, it show that, for buried pipelines, the oil detemperature rate is slow down obviously because of the extending of the zone influenced by temperature drop with the shutdown time going, and the initial oil temperature has no effect on the size of the zone influenced by the temperature drop if the soil properties are well-proportioned. In addition, decreasing the soil rectangle solving area properly can reduce the amount of calculation while ensuring the results exactitude. The oil temperature profile in the pipe during shutdown process was studied. And with the shutdown time goes by, high temperature area which lie upper inside the pipe as the result of natural convection after shutdown would move adown gradually to the lower part inside pipe for buried pipeline.