Study On The Commissioning Process Of The Nu River Crossing Section Of The China-Myanmar Crude Oil Pipeline

In the process of putting into operation,the pressure and potential energy conversion during climbing and downhill will aggravate the phenomenon of gas accumulation at the peak and slack flow under the influence of relatively high elevation and severe undulating terrain.In severe cases,it will cause the water hammer and air blocking,and the accelerated movement of the liquid after the higher places will cause more impact on the low point of the pipeline,which will endanger the safety of the pipeline.For the Nujiang crossing pipeline of the Zhongmian crude oil pipeline with a relative height difference of 1480m located in Yunnan Province,the above-mentioned comissioning problems are particularly significant.To solve this series of problems,it is necessary to theoretically demonstrate and analyze these operation conditions.However,at present,there is a lack of relevant criterion and norms for guidance at home and abroad.Therefore,combining the actual cases of the Nujiang crossing pipeline of the Zhongmian crude oil pipeline to study the influences of the big drop on the commissioning of crude oil pipelines is of great significance to ensure that the pipeline is always in a controlled state,so that the pipeline can be safely and smoothly put into operation and provide theoretical basis and guidance for the commissioning operation of such big drop pipelines.According to the actual terrain conditions,the nature of the crude oil transported,the distribution of resources,etc.,the comissioning method of the Nujiang crossing pipeline is designed to a mode of the crude oil replacing water after partial water filling.The process is divided into the water filling stage and the oil injection stage to conduct multi-phase flow transient simulation and finite element pipeline stress analysis,and the following important conclusions are obtained:1)In the pipeline with big drop and hilly terrain pipe,when the empty pipe filled by water,if the air accumulated at the peaks is not discharged in time,there will be serious slack flow and always be gas slug in the downhill section like the end of the pipe.2)A severe slug flow will gradually form at the end of the pipeline with the increase of the flow.The transition to the severe slug flow will lead to severe fluctuations in the pressure and flow velocity at the end of the pipeline,but when the flowrate is large enough,the flow regime will change too rapidly to cause fluctuations.According to this,the volumetric flow of water filling process in the Nujiang crossing pipeline should be avoided between 2000m3/h-2500m3/h.3)For big drop pipeline with a relative height difference of 1480m and a diameter of 813mm,the larger the volumetric flow is,the higher the impact force of the water on the bottom of the pipeline.However,for a fully buried pipeline,the impact force has little effect,but the weight of the transport medium--water has a certain influence on the bending stress of the pipeline.4)The oil-water interface isolation ball(pigging ball)will increase the intake air of the upstream pipe behind the isolation ball to a certain extent,but it can also effectively reduce the volume of mixed oil and slug flow,the amount of bubble retention in the pipe will also be greatly reduced.5)For drainage work in the big drop pipeline,the larger the drainage aperture is,the faster the drainage efficiency and the better the drainage effect,but the cavitation at the peak caused by drainage will be more intense,increasing the risk of water hammer.According to the theoretical results obtained from the analysis of this paper,the production suggestions and schemes for the production process of the Nujiang crossing pipeline of the Zhongmian crude oil pipeline are provided and used in the engineering practice.The good production results are obtained,which provides a theoretical basis for the comissiong of the crude oil pipeline with big drop and hilly terrain.