THERMAL STATE OF OIL PIPELINES IN DISTURBED SOILS

Abstract

In the course of underground pipeline laying in abnormal conditions the compacted soil is inevitable disturbed, which leads to alteration of its physical and thermal parameters. As a result, pipeline factual operation modes will not correspond to design ones. At the design stage of pipeline it is important to correctly determine expected value of thermal conductivity of soil. Thermal and physical parameters of backfill soil not only differ from initial ones, but also alter during pipeline operation. Change of surrounding soil humidity also affects the heat exchange of «pipeline - soil» system. The closer the pipeline zone is to the northern regions, the stronger is influence of these factors. Soil restructuring lasting differs and proceeds depending on its constitution, condition, associated hydrological and geocryological processes, etc. In this paper, we consider the dependencies that can be used in calculating the tempera-ture state of underground pipelinein backfill soil with adjusting density and varying humidity. Density of disturbed soil is adjusted according to Temporary Instructions 102-2-88 (VI 102-2-88). As an example, a section of an underground oil pipeline laid in the North European part of Russia in loamy soils was considered. The process of backfill soil restoring and change of density and thermal conductivity under constant and varying humidity are shown. The temperature in the final section of the pipeline is determined under the condition of its surrounding soil operation and design parameters, taking into account the soil decompac-tion and humidity change. In soils with low values of adhesion coefficients, the pipeline is subjected to uncalculated thermal effects, which leads to an unstable state of construction, with a change in the pipeline axis position and loss of stability. Therefore, the heat exchange calculation of the pipeline with the environment, changes in the properties of the surrounding soil taken into account, is necessary at the design stage.