Stress-Strain Assessments For Buried Oil Pipelines Under Freeze-Thaw Cyclic Conditions

In this study, outdoor freeze-thaw cyclic tests on the Q345 steel pipeline portion were conducted to analyze the buried oil pipeline stress evolution in a seasonally frozen soil area, namely, the Mohe-Daqing portion of China-Russia crude oil pipeline. The results obtained show that under the freeze-thaw cycle, the variation trend of soil temperature around the pipeline exhibited a hysteresis pattern, which was similar to that of atmospheric temperatures. The soil frost heaving force was shown to drop with depth, and its value at the pipe top was higher than that at the pipe bottom. With the number of freeze-thaw cycles, the frost heaving force of the soil first increased and finally stabilized, while the principal stress of the pipeline increased gradually, and its extreme value tended to be stable after 7-8 cycles, which was consistent with the "ratchet effect" theory. The above findings made it possible to elaborate on a more efficient freeze-thaw cyclic test setup for clarifying the mechanism of frozen soil/pipeline interactions.