Analysis Of Defective Reaction Of Buried Pipes Containing Volume Defects In Faults

With the groth of bured long-distance gas pipeline’s service time, the problems of pipe weld defetcts, stress corrosion cracking will be more serious. In recent years, earthquakes occurd frequently, which caused great impacts of buried pipelines crossing active fault segments. Currently, the study of corrosion pipelins focus on non-seismic condictions, the research of pipeline’s reaction under seismic conditions targeted at non-defectice pipes mostly, there are few studies of reactions of buried pipelines contains corrosion defects under faulting. Under this background, this paper selected buried pipelines contains volumetric defects crossing faults as target to study the reactions under active faults movement, the main contents are as follows:(1) Elaborate the development and research status of pipeline safety assessment methods containing defects both at home and abroad comprehensively, also elaborate the research results of responses of buried pipelines under earthquake, described the background and significance of the research on buried pipelines containing volumetric defects under fault movement and listed the research contents in this article.(2) Introduce the basic theory of plasticity limit in the current safety assessment standards of pipelines contains defects. Discribes the calculation methods of pipeline failure stress and failure stress in ASME B31G and DNV RP-F101evaluation criteria, which are the most representative standads of pipeline with defects. At last, introduce the standardized treatments of volume type corrosion defects.(3) Summarized the damage formations of buried pipine under earthequake, cited the basic axial and transverse vibration equations of buried pipelines under seismic waves. Also summarize the main structues of faults, analysised the different damage types of buried pipelines under fault movement.(4) Created finite element model of buried pipelines with volume type corrosion defects based on finite element theory and nonlinear theory, using Solid45unit to discrete pipe, using a three-fold model to discrete the mechanical properites of the pipe material and using Drucker-Prager model to dicrete the mechanical properites of buried soils, established the nonlinear contact model for pipe-soil by conbin39unit, applied loads on the pipe according to the buried gas pipeline actural operating environment and faulting form, confirmed boundary conditions and computing areas based on the stress and strain distribution characteristics of buried gas pipeline under the movement of faults, contribute the three-dimensional finite element model of pipeline with volumetric defects crossing active faults which considering multiple non-linear relationships.(5) On the basisment of the results of the finite element model of buried pipeline with defects, analysis the factors including defects depth, areas, locations, buried soils and pressure affecting the impacts on the seismic capacity of buried pipeline, discussed the effects of different factors on the stress and strain distribution and peak on the top and bottom of pipe, combined with pipe circumference fracture stress formula in ASME B31G standard, analyzed the seismic safety of buried pipeline with defects in different corrosion parameters.(6) Summarized the most commonly used measure of buried pipelines earthquakeEngineering and general support measures, proposed specific measures for seismic retrofitting for the example pipeline, described the technical means used pipeline seismic monitoring and early warning system and pipeline earthquake emergency system.