Analysis Of Mo-Da First Line Temperature Field And Structural Safety Evaluation

The first line of Mo'he-Daqing section of the China-Russia crude oil pipeline is one of the important energy cooperation projects of the Belt and Road,whose stable and safe operation promotes the national development both economically and strategically.Since the Mo-da First Line was put into production in 2011 with an original design temperature of-6.41 ? ? 3.65 ?,the maximum oil temperature has risen to 20.58 ?,which will possibly continue to rise in the future and intensify the risk of thawing.Besides,after the Mo-da Second Line is commissioned in 2018,an increase in the risk of thawing corresponds to the interaction of these two pipelines with the passage of time.Therefore,there is an urgent need to evaluate and predict the safety of the Mo-da First Line in the early and medium term.In this paper,Fluent is used to establish the mathematical model of the soil temperature field around the buried pipeline of the Mo-da First Line.The effects of oil delivery temperature,pipeline depth and insulation layer thickness on the soil temperature field were studied respectively,in order to summarize a set of prediction methods of quantizing soil maximum melting depth.Results showed,the continuous increase in oil temperature has great effects on the soil temperature field around the buried oil pipeline in the frozen soil area.The melting depth increases with the increase of the pipeline depth while decreases with the increase of the thickness of the insulation.Based on the acquired maximum melting depth,the finite element software ABAQUS was utilized in this work to establish the stress and strain model of the pipeline.The effects of the melt settlement deformation,the wall thickness and the internal pressure of the pipeline on the pipeline strain were analyzed,and a set of quantitative pipelines was established.The study believes that the strain of the pipeline increases with the increase of the melt settlement deformation,and decreases with the increase of the wall thickness of the pipeline,and the internal pressure of the pipeline has little effect.Finally,the effectiveness of thermosyphon technology to reduce the risk of pipeline melting was studied.In this process,the temperature field model of the soil around the pipeline with thermosyphon was established by Python and imported into ABAQUS for numerical simulation.The results showed that the effective cooling radius of the thermosyphon is about 1.75 m,and the thermosyphon technology reduces the risk of soil thawing around the buried oil pipeline in the frozen soil area.At the same time,the actual arrangement of the thermosyphon was studied.When the distance between the thermosyphon and the center of the pipe is 1.5m,the cooling effect is optimal.The greater the distance between adjacent thermosyphons on the same side,the greater the depth of thawing in the frozen soil layer,and its influence increases with the increase of pipeline operation time.Therefore,this study can offer a reference for the application of thermosyphon technology.