Study On The Safety Assessment And Structure Strength Of Triple Valve Plugging-seal-off Components Used In Shan-jing Gas Pipeline

The plugging-seal-off technology of petroleum-gas pipeline is necessary and very important for repairing pipeline leaking & pipeline route altering. The plugging triple valve is a comparative essential component, for it will exist forever with the pipeline. If it can not work in gear, the consequence will be too dreadful to contemplate. Foreign countries forbid the technology to us for years, our relative units design it by experience merely without a concrete theoretical base. Moreover the weld and installation of the triple valve can not stop the pipeline transportation, so stipulating severe weld criteria is vital. In a word, the science value and significant is crucial, the research will surly prompt and consummate our plugging technology.The main task & achievement of the research contains several aspects:(1)Using elastic stress analytic method to design the triple valve flange of the stopper.For this flange take a special strypped-down(be notched for metal hoop) and the technics is unique, so we took a low stress level.(2)ANSYS(large-scale finite element software) is adopted. We set up the three-dimension finite element contiguity model of the triple valve flange of the stopper and ring clip as well as the linearity aggrandizement of elasticity—plasticity. It simulates the real conditions and the trend of change in stress-strain field. (3)To attain the optimum position of slot, we take optimization plan to select 8 different slot positions separately , Then analyzed them detailedly using FEA method. The concrete process is as follows:Firstly, we selected four possible dangerous profiles on the basis of the model symmetry and defined the shortest line between two surface of the dangerous profiles as stress category line. We deal every hefts on the stress category line according to equality and ponderance linearity, then took stress category assessment. The mean stress after average disposed is membrane stress. After ponderance linearity disposed, the linearity of the stress is the quadratic stress, the rest is peak value stress. Then assessing the intension by the Mises strength theory. The results showed all the 8 kinds flanges can satisfied the safety need. The biggest Von Mises stress is on the joint of the ring clip and flange, the phenomenon is caused by concentrative stress, the range is very limited and is not the reason lead to invalidation. The stress on the flange ring slot is comparative high, the stress on screw hole is relative low. Although the stress on the joint area of the flange cone and column is high, the stress is not the biggest, the traditional elastic method is not correct here. The biggest stress around here is on the cone. The special load form and the huge bending moment which caused by far away from the fixed point are the primary reason. (4)The weld and installation of the plugging triple valve is first step of the plugging procedure. There are two major steps: First, the welded butt joint between the upper and lower backplates. Second, the angle weld of the upper lower backplates and pipeline. The material of the upper and lower backplates is low-grade alloy high hardness steel Q345, but the pipeline is X60 (API SPEC 5L), its yield-strength is 413MPa, is also low-grade alloy high hardness steel. We reckon several parameters, such as : weld method, bevel condition, welding rod type, welding parameters. Lots of welding procedure has been done, the homologous welding procedure assessment was undertaken, the eligible welding procedure was stipulated eventually.