Safety Evaluation And Risk Prevention Study On Pipeline With Third Party Damage In Changqing-Hohhot Line

The dissertation carries out study on pipeline damage and leakage diffusion process in Changqing-Hohhot gas pipeline. It is an urgent problem in Changqing-Hohhot gas pipeline to establish more accurate replacement criterion for pipeline with dent, propose security assurance measures and formulate leakage & diffusion control plans and emergency plans in high consequence areas. Through literature review and field data collection, the research content and research route are put forward. The main content and results of the dissertation are as follows:(1) Based on the research findings of pipeline with Third-party Damage (TPD) and the theory of High Consequence Area (HCA) recognition,15 areas with high consequence are obtained after scoring the pipes, which provides basis for safety evaluation and risk prevention & control in Changqing-Hohhot gas pipeline.(2) Chemical composition analysis, tensile property test, Charpy impact test, hardness test and metallographic analysis are carried out with respective to pipeline in High Consequence Area. Experimental results indicate that the tensile property of straight pipe and impact property of circumferential weld meet the requirements, but there exists corrosion at repairing welded joint which is the dangerous part of pipeline. Experimental results can provide necessary data for finite element analysis.(3) A finite element model of bucket tooth damage is established based on the theory of non-linear dynamics and mechanical boundary condition of pipeline third-party damage. The model simulates four working conditions namely, normal transportation, bucket tooth impacting pipeline, unloading of bucket tooth and unloading of pipeline internal pressure. It also analyzes the influence of impact angle and biting depth on stress, strain, the maximum depth of dent and degree of damage.(4) Based on 6% critical strain value and the maximum depth of dent after third-party damage, the relation of thickness and dent depth and maximum stress, strain, impact force and biting depth is established. Then, the replacement criterion of pipeline with third-party damage is proposed, which can help make fast and scientific decisions for pipeline replacement to ensure long service of pipeline.(5) Aiming at macroscopic cracks and holes by third-party damage, researches on gas leakage, diffusion and explosion are carried out. Then take high consequences areas of Changqing-Hohhot gas pipeline in Yi Li Ershijia pasture for example, a Computational Fluid Dynamics (CFD) model of gas leakage and diffusion is established using large eddy turbulence. The leakage and diffusion regularity of small and large holes are studied.(6) The effect of wind speed on gas leakage and diffusion is considered through CFD simulation. With the increase of hole size, jetting speed of gas decreases, and diffusion range and near-ground diffusion speed increase when leakage rate increases. The simulation results indicate that there could be explosion when natural gas diffuses to constructions. Finally, the warning system and security plans of third-party damage leakage are established.(7) Based on the research on pipeline replacement suggestion and leakage & diffusion regularity, prevention, control and monitoring technology of pipeline third-party damage are analyzed. Finally, maintenance and replacement technology and process of third-party damage pipeline in Changqing-Hohhot gas pipeline are proposed.