Research On Ductile Damage Of Thin-walled Stainless Steel Gas Pipeline With Simple Depressions

China is in the era of natural gas pipeline network,which covers over 500 million people.It is the largest natural gas network in the world with the largest population and the largest area of radiation.Maintain a high level of pipeline integrity and reliability is priority to ensure the safe operation of the pipeline network system.The mechanical damage is the main culprit of frequent pipeline accidents.Dent defect is one of the most common types of mechanical damage.In recent years,the thin-walled stainless steel gas pipeline has become a kind of ideal gas indoor pipe material to start up in the gas industry.At present,most domestic scholars in the research field of dent defect of pipe mainly conduct the research work on large size oil and gas pipeline with dent defects.Therefore,it is necessary to conduct a further study on small size indoor gas pipeline with dent defects such as the thin-walled stainless steel pipe,which will be of great significance to guarantee the safe operation of gas pipeline network system.In accordance of plain dent defects on the thin-walled stainless steel gas pipelines,the work done by this paper is as follows:(1)On the basis of fully collecting references at home and abroad,a brief summarization of the current situation of the development of thin-walled stainless steel pipe and the research status of dented pipeline was made.Thus,the research contents,technical route and the feasibility of demonstration method in this paper were presented.(2)The basic properties,connection modes and application advantages of thin-walled stainless steel were illustrated,and the definition,classification and detecting techniques of dent defect were briefly summarized.Then,one uniaxial tensile test and one surface strain tensile test for thin-walled stainless steel gas pipeline were carried out,the basic performance parameters and the material constants involved in ductile fracture criteria were obtained.(3)Made a generalization of the common ductile fracture criterions in engineering,selected the most applicable criteria-Oyane ductile fracture criterion.For the single plain dent on the thin-walled stainless steel gas pipelines,based on the nonlinear contact theory,the finite element pipepline model was established using ABAQUS software.Having simulate the pipeline pressed by the spherical indenter which can formed dent defects,then based on Oyane ductile fracture criterion,on the condition of different indenter sizes,different pipeline sizes and different operation pressure,the relationship between dent depth and the damage degree of dented pipeline was analysed.In addition,using regression method to analyse the simulated results by SPSS software,then get the concrete expressions in range of application.Finally,after removing the indenter,the situation of spring-back and residual stress in dent area was analyzed.(4)For the Coaxial double plain dent on the thin-walled stainless steel gas pipelines,two suitable pipeline lengths were determined through hundreds of finite element calculation,which were respectively used to study two working conditions,the one is affected by consolidation,another one is not.Then one pipeline model was setted up by using the length which isn't affected by consolidation as standard,imposing two coaxial distributed dent defects which are isometric to both ends on pipeline model.And have calculated the Von Mises equivalent stress on the pipe wall caused by dent defects of 8 groups of different depth on condition of different space,the influence law of the interaction between two plain dent defects and the stress distribution law of the pipe wall were analyzed.Finally,the maximum effective distance of dent defects in each group was determined.After that,two pipeline models were setted up by using length affected by consolidation as standard,respectively having impose two coaxial distribution dent defects which are distant from both ends of equidistance and un-equidistance on pipeline model.Under the condition of different space,respectively having calculate the Von Mises equivalent stress on the pipe wall caused by dent defects of 8 groups of different depth.An analysis on the unbalanced influence and balance influence was carried out and the stress distribution law of the pipe wall was obtained.In the case of different parameters changing,the plain dent defects on the thin-walled stainless steel gas pipeline were studied,which provides a theoretical basis for the safety design and safety maintenance of the natural gas pipeline network.