Research On Defect Tolerance Limit Under Expected Life Of Ultra High Pressure Vessel Head Based On Stress Partition

Different types of defects may occur in the process of production and manufacturing of ultra-high pressure vessel pressure equipment.Stress concentration will occur in the defective parts under the action of actual service load,resulting in the occurrence of crack defects.Crack defects are a common and easy to cause serious harm in the defects of pressure equipment.Under life expectancy pressure load,different types and distribution of cracks have different tolerance limits,which will have different effects on the anti-fatigue performance and service safety of pressure equipment structure.Therefore,the zoning evaluation of the allowable limits of typical defects under life expectancy has become a very meaningful study for the safety evaluation of defects in ultra-high pressure vessel equipment.In this thesis,the ultra-high pressure vessel head of a high-pressure vessel company is taken as the research object,and the theoretical analysis of defect fatigue propagation and the simplification of typical defects are carried out.Based on stress partition,Abaqus and FRANC3 D finite element analysis software,the allowable limits of surface defects and deep buried defects of ultra-high pressure vessel heads under the condition of expected life were designed and analyzed.The main work contents are as follows:(1)The fatigue evaluation theory of crack defect was summarized and analyzed,and the co-simulation analysis method of crack defect fatigue propagation was introduced and verified,which proved that the method was accurate and feasible.Based on the application of stress superposition principle in FRANC3 D software,the calculation of fatigue extended stress intensity factor of defect at complex contact surface is solved,the calculation speed is greatly improved,and the accuracy of solution is verified theoretically.(2)The blank parts of pressure equipment for ultra-high pressure vessels and their defects in production and use are summarized and analyzed.Based on the content of GB/T19624-2019 "Safety Assessment of Pressure Vessels with Defects in Use",the surface defects and deep-buried defects of ultra-high pressure vessel heads in practice are dealt with regularized.(3)ABAQUS finite element software was used to build a numerical calculation model for the dynamic service process of the ultra-high pressure vessel head,and then the strength was analyzed.According to the analysis results,the ultra-high pressure vessel head was divided into stress zones to determine the stress concentration zone,non-stress concentration zone and experience zone under the load,and the defect zone evaluation model was proposed.(4)On the head of ultra-high pressure vessels containing defects in the cycle of life expectancy of 100000 pressure load,the stress clusters,the stress in clusters,experience in typical defect tolerance limit,then discusses the superhigh pressure vessel head performance and its inner relation between defect tolerance limit,finally realizes the life expectancy of typical defect tolerance limit partition evaluation design.The allowable limits of point defect,continuous defect,etch pit defect and deep buried defect located in different stress zones are given.The study of allowable limit of defect zone evaluation can provide important theoretical basis and method for defect detection and safety evaluation of such ultra-high pressure vessel pressure equipment,which has certain academic value and engineering application value.