The Thermodynamic Analysis And Simulation Computation On Buried Hot Oil Pipeline Service

The northeast (NE) hot oil pipeline has been running for 30years far more, and its using life has exceeded the designing life. Corrosion protective covering breakage and oil scattering are very common. According to the strategic planning that safe running at present and the market of transport crude oil with boosting pressure in the days to come as well as smooth and steady operation for 20years after reconstruction, it urgent needs to be serviced. During the process of service, the thermodynamic property occur alteration with the changement of oil properties, which will have influence on well proceeding of restartup. Therefore, it is necessary to study on the thermal process of sevice in different operational modes and restartup.On the basise of taking the annual period alternation of the air temperature and the influence of soil temperature field around hot oil pipeline into account, with calculating frictional heating and analysis the influence of wax precipitation thermal resistance on coefficient of heat transfer, the thermodynamic and hydraulic models of wax buried hot oil pipeline operation were established, which can offer initial conditions for the pipeline service.The unstable state thermodynamic model of the process of pipeline excavation and shutdown was developed by using of equivalent conduction coefficient in liquid phase. The models of thermodynamic allowance maximum excavation length were shown in two operational modes that are operation and shutdown and they were calculated by binarydivisive procedure. The definition modes of allowance shutdown time and the danger arrow were established. Taking the availability of excavation segment during the process of service into account, the thermodynamic and hydraulic mathematics models of shutdown and restart up of the service hot oil pipeline were established.The startup flow capacity was obtained by adopting Sukhov modifier formula. The restartup pressure was calculated by pressure wave model and friction resistance model respectively. The alternation regularities of oil temperature were analysed in excavation segment during the period of shut down with different service parameters. Comparing running data with test data of QingHa buried hot oil pipeline, stable state operation models were proved to be right. And an experimentation of shut down and restart up of the oil pipeline was done at the base of Daqing oil-gas field engineering. Calculate the pipeline by software and contrast the results and test data to prove the model being right. The software named"Simulation software for hot oil pipeline service"was developed to calculate numeric value, which can compute the axis direction temperature, radials direction temperature, startup pressure, allowable shut down time, and danger arrow of the pipline son on.At last in view of LinYuan station to Tai Yangsheng station, simulation computation was done and correlation service suggestions were given. For NE pipeline, the optimum season of excavation service after shutdown is May, and the optimum season of excavation service in operation state is October. When the distance between excavation starting point and Lin Yuan station is more than 6.8km, excavation service after shutdown can not be directly carried, it needs to enhance outlet temperature. If the excavation starting is LinYuan satation and the seaon is May, the allowance shutdown time is 10h, if the excavation starting is 40km away from LinYuan satation, the allowance shutdown time is 6.7h.