It is common to have a wax layer on the inner wall of waxy crude oil pipeline. However, the study of the wax layer on the heat transfer of buried pipeline systems is inadequate due to its instability of composition and properties; it may lead to the inaccurate prediction of the pipeline temperature field. Based on the finite element simulation technology, a three-dimensional heat transfer model of buried crude oil pipeline involving wax layer was proposed and solved. The thermal effect of the wax layer on pipeline system was analyzed quantitatively. Numerical results show that the average deviation of soil temperature near the pipeline reach 1.42 K when there is a 4 mm wax layer. Among different thermal conductivity models of heterogeneous materials, the EMT model plays best in predicting the conductivity of a waxy layer. By setting different working conditions, the influence mechanisms of several thermal influencing factors are discussed. The results show that the thermal influence range of heated pipe is positively associated with oil temperature and velocity. The core thermal response zone is about 12 m along the X-axis. Beyond 8 m depth from ground surface, the temperature fluctuation of soil is almost unaffected by the oil pipeline.

Crude oil pipeline transportation is usually a closedprocess undera certain depth of burial, and the condition of oil in the pipelinechanges with the continuous decline of temperature during the transportationprocess. The safety and energy consumption of pipeline transportationare closely related to the accurate prediction of oil temperature.It is a popular technique to use the thermally affected region toovercome the problem of an unclosed calculation domain caused by thesemi-infinite soil around the pipeline. However, there is no clearand unified guidance on the thermally affected region at present,and improper region size may lead to a loss of the accuracy of thepipeline system. Therefore, our study answers two questions aboutthe optimal form of the thermally affected region and its economicscope of application. The coupled solution of heat transfer and flowin a tridimensional numerical model is carried out, and the thermodynamicinfluences of the geometric shape and range of the thermally affectedregion on the buried pipeline system are investigated. The resultsshow that the rectangular region is more suitable for the modelingof buried oil pipelines, and a region with 16 m width and 9 m heightis recommended for the conventional case.