Girth Welding Simulation Of Nickel-based Alloy And Application In Structural Failure Assessment

There should be enough sufficient margin in nuclear reactor pressure equipment design.It is to ensure that the pressure boundary will not fail under any normal operating conditions and expected operating events.The safe operation of nuclear power plants is affected by the structural integrity.Welding is also a key process in the manufacture of nuclear pressure equipment and the existence of welding residual stress makes the welded parts more weak to failure.There are many high-temperature mechanical devices in TMSR that is designning and constructing by Shanghai Institute of Applied Physics,Chinese Academy of Sciences.As for the service safety of high temperature equipment,appropriate and effective methods should be adopted to analyze and evaluate the structural integrity of equipment during service period.It is to determine whether the equipment with defects is safe or not,and to provide suggestions for equipment design and operation and maintenance.In this paper,numerical simulations of nickel-based alloy girth weld welding and post-weld heat treatment were carried out by finite element method using ABAQUS software in the engineering background.The failure assessment of pressure vessel structure is also studied in combination with BS7910-2013 ?Guide to methods for assessing the acceptability of flows in metallic structures?.The main research contents are as follows:1)Study on Numerical Simulation of residual stress in girth weld of nickel-based alloy pipeline.The loop pipeline in the simulation reactor(TMSR-SF0)is studied in the research.TMSR-SF0 has been studying by Shanghai Institute of Applied Physics,Chinese Academy of Sciences for years.Welding process of pipeline was simulated numerically.Firstly,the reliability of the simulated results of girth welding is verified,then the variation trend of residual stress and deformation in axial and circumferential welding with the change of D/B ratio of inner diameter to thickness is investigated.It is found that the ratio of inner diameter to thickness affects the residual stress and deformation of welding.2)Simulation of post weld heat treatment of pipeline girth welding.According to Norton creep law,the residual stresses of post-weld heat treatment at different holding time were analyzed.The model is D/B=1 girth welding.Then the appropriate creep activation energy was selected to obtain the parameters of Norton equation at 760 ?.The corresponding post-weld simulation was carried out to investigate the effect of different holding temperature on the reduction of welding residual stresses at the same holding time.It provides a meaningful reference for the optimization of post-processing technology of nickel-based alloy welding.The residual stress can be effectively reduced in a short time by choosing the appropriate holding temperature.3)Research on failure stress analysis method of structures with defects.According to the British structural integrity assessment standard BS7910:2013,considering the influence of welding residual stress,FAD(Failure Assessment Diagram)failure assessment method was used to evaluate the safety of welded parts containing internal surface cracks on the cylinder of nickel-based alloy pressure vessel.Firstly,the finite element method(FEA)was used to simulate the girth multi-layer and multi-pass butt welding of V-groove and X-groove of pressure vessel;The distribution of welding residual stress was obtained.The residual stress curve of V-groove butt welding was compared with the standard residual stress distribution of BS7910:2013.Secondly,the formula of BS7910:2013 grade 1-FAC(Failure Assessment Curve)curve is deduced,and the failure stress of the semi-elliptic crack in the axial direction is predicted by considering the influence of residual stress,stress concentration and plastic failure factor at the welding position.Residual stress distribution directly affects the value of failure stress,and the failure stress at the weld center line obtained by finite element simulation method is conservative,which can better ensure the safety of Engineering reference.