Research On Effects Of The Increase Of The Oil Temperature Of Buried Pipelines On The Thaw Settlement In Permafrost Region

The China-Russia oil pipeline crossed most parts of frozen soil in northeast China with the oil temperature much higher than the design temperature.And it is predicted to rise to 30oC.The increase of the oil temperature will lead to thaw settlement,so the safety of the pipeline will be greatly challenged.In this research,a temperature field model of the buried oil pipeline in permafrost region was established using the FLUENT software.The effect of the increase of the oil temperature under conditions with different values of surface temperature,pipeline buried depth,insulating layer thickness and water content was analyzed by setting the oil temperature as the design,present and predicted temperature.On the basis of the empirical model,the thawing deformations under conditions with different water contents were derived.Strains of the pipeline under the effect of thaw settlement before and after increasing the oil temperature were calculated using the finite element software ABAQUS.According to strain-based design guideline,the failure analysis of the thaw settlement led by oil temperature increasing was conducted.Finally,the temperature field model with thermosyphon was built for the condition where the strain demand is bigger than the strain capacity for analyzing the effectiveness of the thermosyphon.It is shown that the increase of the oil temperature has a greater effect on the frozen soil with a higher surface temperature and a higher pipeline buried depth.The pipeline with a thicker insulating layer can run with less failure possibility,and the slightly thinner insulating layer can't insulate the heat well in the later stage.The increase of the thawing depth is bigger when the water content is low,and the influence of the increase of oil temperature is greater.Aiming at the conditions where the thawing deformation is bigger than the allowable value,some measures should be taken to control the freezing damage.To set pairs of thermosyphon along the pipeline is able to prevent the expansion of thawing cylinder and provide guarantee for the safe operation of the pipeline.