The article deals with the issues of increasing the accuracy of hydraulic calculation of oil and oil product pipelines. A brief historical review of dependencies for determining the coefficient of hydraulic resistance obtained as a result of industrial tests of operating pipelines is given. It is shown that the existing methods of hydraulic calculation for most of the operated pipelines do not allow achieving the coincidence of the actual and calculated values of the hydraulic resistance coefficient with the required accuracy. This is due to the uncertainty in assessing the state of the internal surface of the pipeline and the presence of additional hydraulic resistances caused by accumulations of water and air at the points of bending of the route profile. The authors carried out a comparative analysis of the most common theoretical dependencies for calculating the coefficient of hydraulic resistance in the mixed friction zone of a turbulent regime with the results of semi-industrial and laboratory tests of pipelines given in the literature. It is shown that when using the value of the relative roughness of the pipe wall adapted to the actual pumping conditions, operational calculations can be performed with the required accuracy practically according to any of the formulas of classical hydraulics. At the same time, based on the literature data, it was concluded that the actual value of the relative roughness in the formulas for the hydraulic calculation is not as important as the correctly found empirical coefficients. From here follows a conclusion: for specific technological sections of operating oil and oil product pipelines, there is no need to use such a parameter as relative roughness. To improve the accuracy of operational calculations of specific technological sections of operating oil and oil product pipelines, the authors proposed not to use a deliberately undefined value of relative roughness in the calculations, but to approximate the industrial test data with empirical dependencies, the coefficients of which will integrally take into account all available hydraulic resistances. As an example, the authors approximated the experimental data for two technological sections of an operating oil pipeline by the dependences of the hydraulic resistance coefficient on the Reynolds number. It is shown that the most preferable approximation of the dependence of the hydraulic resistance coefficient on the Reynolds number by a polynomial, the degree of which should be justified in each specific case.
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