Research On Safe Pigging Technology Of Large Drop Natural Gas Pipeline

The Sino-Myanmar natural gas pipeline begins in the southern coast of Myanmar.It travels through Yunnan-Guizhou-Guangxi area in China.The terrain of whole line is mostly hilly and mountainous,so there are many hilly pipelines along the pipeline.Influenced by the topography,the liquid accumulates in the pipeline with hilly pipeline,which is easy to form slug flows and reduce the cross-sectional area of pipeline,thus reducing the gas transmission efficiency.In order to eliminate the influence of liquid,it is necessary to clear the hilly natural gas pipeline at regular intervals.In the process of pigging,the pressure along the pipeline and the pigging speed are different from those in the flat area.The main manifestations are that the pressure and the pigging speed fluctuate in the downhill and downhill segments,and the fluctuating range is larger than that in the flat area.Especially in the downhill section of the pipeline,due to the gravity effect,the speed of liquid and pig is gradually accelerated,and the pig directly impacts on the bottom of the pipeline with the high speed.When the speed of the pig reaches a certain value,the strong impact will cause structural instability and rupture failure of the pipeline.Aiming at the problem of the pigging in the hilly natural gas pipeline,taking Longling-Midu section of China-Myanmar natural gas pipeline as the research object,using OLGA and PVTSIM software to simulate the working conditions,this paper analyzes the changing regularity of the influencing factors in the process of pigging,explore the safe speed of the pig,and put forward the safe pigging scheme,which is of great significance for ensuring the safe operation of hilly pipelines.The main research contents and important conclusions of this paper are as follows:(1)Based on the results of literature investigation,the main field operation parameters of Longling-Midu hilly pipeline are determined.PVTSIM software is used to analyze the fluid properties of the hilly pipeline that is imported to OLGA software.The OLGA software is used to establish the whole pipeline model and simulate the process parameters along the pipeline.The numerical simulation results of the process parameters along the line are compared with the field data,and the results show that the numerical simulation can accurately reflect the variation law of the operating parameters along the line,which verifies the correctness of the simulation model.(2)According to the pipeline model established by OLGA software,the transient mathematical model of pigging is loaded to carry out the numerical simulation of pigging in longling-midu section without and with accumulated liquid,and to analyze the change rule of the pressure,the velocity of pig and the volum of accumulated liquid.The results show that if there is no accumulated liquid in the pipe,the maximum velocity of pigging reduces with the increase of outlet pressure when the flow rate is the same,and increases with the increase of flow rate when the outlet pressure is the same;the pressure variation with and without accumulated liquid in the pipe is not much different,but the velocity fluctuation of the pig is larger along the line if there is accumulated liquid in the pipe.(3)Based on the results of numerical simulation of the pigging process and combined with the maximum allowable operating speed of the pig under the ultimate load of the pipe,the safety pigging schemes of Longling-Midu pipeline with or without liquid accumulation are formulated.The results show that the maximum allowable operating speed of the pig is 11.3 m/s,and the maximum speed of the pig is under 11.3 m/s in all working conditions without accumulated liquid,so the pigging scheme is to pig when the pipeline transportation efficiency is less than 95%;if there is accumulated liquid in the pipe,when the velocity of the pig reaches the maximum allowable operating speed,the pressure difference between the inlet and outlet of pipe is taken as the safe pigging time under each working condition,and a total of 15 pigging schemes are put forward.