Evaluation Of Flow Safety Of Long - Lived Crude Oil Pipeline

The safe operation of the crude pipeline which transports the high freezing point and waxy oil is always one of the most important issues that the petroleum industry focuses on. Traditionally, inlet temperature higher3degree than freezing point is utilized to judge whether the pipeline is safe, however, the judgment can’t quantify the safe allowance of the pipeline, and sometimes it will cause the excessive energy consumption. Consequently, it was of great significance to the pipeline’s safety to use the uncertainty analysis method to study the flow safety problem of pipeline and quantify the safe allowance. The software whose name is "the system to evaluate and manage the crude pipeline’s flow safety based on reliability" quantifies the safe allowance by calculating the probability of the pipeline work into unstable workspace or failing restart. In the process of calculation, the distribution of the factor which influences the crude pipeline’s flow security generally uses the normal distribution, and the average hydraulic wax deposition thickness is used as paraffin deposit thickness, which reduces the accuracy of the evaluation results. Therefore, a further study about how to evaluate the crude pipeline’s flow safety has been done, taking the Chang-Hu oil pipeline as the research object, aimed at solving the existing problems and improving the accuracy of the evaluation results.Firstly, according to the site operation data of Chang-Hu oil pipeline, based on the analysis of the sensitivity of uncertain factors on the critical flow, the results show that:the out station temperature, heat transfer coefficient and the ground temperature have great influence on the critical flow rate, and the average hydraulic wax deposition thickness has little effect on the critical flow. Based on the study, the probability distribution of uncertain factors which have greater influence on the critical flow has been determined.Secondly, because of the difference of average hydraulic wax deposition thickness and actual wax thickness, the average hydraulic wax deposition thickness which is used in traditional process of evaluating can not accurately reflect the actual situation of the pipeline. Chang-Hu oil pipeline mainly transport waxy crude oil, affected by the crude oil transportation mode in different seasons, the wax deposition is more serious in summer because of the lower average oil temperature. Therefore, based on the existing method of wax deposition thickness calculation, this paper put forward a method which combined with wax deposition model and actual pipeline pressure drop for wax deposition thickness calculation, and calculate the wax deposition thickness of the pipeline along the route of each station in summer months by using this method, not only reflect the pipeline actual situation of wax deposition, but also correspond with the actual hydraulic regime of pipeline.Finally, considering the non-uniformity of influencing factors of pipeline’s flow safety and the uncertainty of wax deposition thickness along the pipeline, an evaluation about the Chang-Hu oil pipeline’s flow safety in the summer has been done by adopting the software. Through the comparative analysis of the evaluation results, it is found that the evaluation system is partial to the safe side, the evaluation results become more in line with the actual after considering the influence of uncertain factors and wax thickness along the pipeline. According to the flow safety evaluation of Chang-Hu oil pipeline’s summer condition, the level of security for each station and the critical volume has been confirmed, and the safety margin has also been quantified. This paper proposes the corresponding energy saving measures for the higher security stations, such as decreasing the out-station temperature, prolonging the shutdown time; puts forward relevant flow assurance measures for the lower security stations, such as increasing the inlet temperature. This provides the basis for the operation and management of the Chang-Hu crude oil pipeline in the future.