Numerical Study and Economy Analysis of Two Heated Crude Oil Pipelines Laid in One Ditch

In this paper,the transportation economy of two heated crude oil pipelines laid in one ditch is analyzed by taking into account the influence of operating temperature,interval between two pipelines,and distance between two heating stations on the heating energy consumption.To analyze the transportation economy,the two heated crude oil pipelines laid in one ditch are simulated under four operating conditions based on an unstructured finite volume method.Compared with laying two crude oil pipelines separately in two ditches,the results attest notably higher soil temperature,meaning reduced heat dissipation of each pipeline by laying two pipelines in one ditch.It is inferred that for the same desired oil temperature at the inlet of the next heating station,laying two pipelines in one ditch requires lower oil temperature at the outlet of heating station,indicating decreased energy cost at the heating station and improved transportation economy.Then economy analysis of four configurations of laying two pipelines in one ditch is performed.By comparing the results of four conditions,the interval between two pipelines of 1.2 m is found to save the energy most efficiently,which is as large as 26.6%compared with that of laying two pipelines in two separate ditches.In addition,narrowing the pipeline interval and extending the distance between heating stations is beneficial to save heating energy.This study is expected to provide valuable guidance for operation optimization of heated crude oil pipelines.

Mathematical Modelling of the Transient Response of Pipeline

Steam pipelines applied in power units operate at high pressures and temperatures.In addition,to stress from the pipeline pressure also arise high thermal stresses in transient states such as start-up,shutdown or a load change of the power unit.Time-varying stresses are often the cause of the occurrence of fatigue cracks since the plastic deformations appear at the stress concentration regions.To determine the transient temperature of the steam along the steam flow path and axisymmetric temperature distribution in the pipeline wall,a numerical model of pipeline heating was proposed.To determine the transient temperature of the steam and pipeline wall the finite volume method(FVM) was used Writing the energy conservation equations for control areas around all the nodes gives a system of ordinary differential equations with respect to time.The system of ordinary differential equations of the first order was solved by the Runge-Kutta method of the fourth order to give the time-temperature changes at the nodes lying in the area of the wall and steam.The steam pressure distribution along pipeline was determined from the solution of the momentum conservation equation.Based on the calculated temperature distribution,thermal stresses were determined.The friction factor was calculated using the correlations of Churchill and Haaland,which were proposed for pipes with a rough inner surface.To assess the accuracy of the proposed model,numerical calculations were also performed for the thin-walled pipe,and the results were compared to the exact analytical solution.Comparison of the results shows that the accuracy of the proposed model of pipeline heating is very satisfactory.The paper presents examples of the determination of the transient temperature of the steam and the wall.

Simulation study on heat-affected zone of high-strain X80 pipeline steel

The microstructure evolution and impact-toughness variation of heat-affected zone（HAZ）in X80 highstrain pipeline steel were investigated via a welding thermal-simulation technique,Charpy impact tests,and scanning electron microscopy observations under different welding heat inputs and peak temperatures.The results indicate that when heat input was between 17 and 25kJ·cm^（-1）,the coarse-grained heat-affected zone showed improved impact toughness.When the heat input was increased further,the martensite-austenite（M-A）islands transformed from fine lath into a massive block.Therefore,impact toughness was substantially reduced.When the heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was between 900 and 1300°C,a higher impact toughness was obtained.When heat input was 20kJ·cm^（-1） and the peak temperature of the first thermal cycle was 1300°C,the impact toughness value at the second peak temperature of 900°C was higher than that at the second peak temperature of 800°C because of grain refining and uniformly dispersed M-A constituents in the matrix of bainite.