Stress prediction of heated crude oil pipeline in permafrost region via fully coupled heat-moisture-stress numerical simulation and SVM algorithm

Abstract

Large diameter crude oil transmission pipelines in unstable permafrost areas have been put into operation in China in recent dozen years. The perennial positive temperature operation of buried heating transmission pipelines leads to freeze–thaw of the soil around pipelines, and the axial stresses generated by thawing settlement of permafrost may induce fracture failure of weld crack. However, there are many shortcomings in existing frozen soil thawing settlement analysis and pipeline stress assessment methods, which makes it difficult to accurately analyze and predict the axial additional stress of pipelines induced by thawing settlement. Based on heat conduction and permafrost thawing consolidation settlement theory, numerical inversion analysis of centrifuge test was conducted to verify the accuracy of the finite element method. The key influencing factors such as wall thickness, insulation layer thickness, buried depth of pipe, and length of thawing settlement zone on the axial stress and strain state of buried pipeline under the condition of double pipe operation of Mo-da line were investigated. The results show that: Pipeline with an insulation layer, larger wall thickness and smaller buried depth is beneficial to improve the bearing capacity of buried pipeline under thawing settlement of permafrost. The axial stress varies nonlinearly with the increase of the thawing settlement zone length. Based on support vector regression (SVR) model, the axial stress prediction model of pipe crown and invert at different positions in the thaw settlement area was proposed and verified by field monitoring data of buried pipeline. The relative error between the prediction results and the field monitoring results is less than 15 %. This study can provide some theoretical support for the structural design of pipelines in thaw settlement area.