Constraint-dependent J-R Curves Of Dissimilar Metal Welded Joint For Connecting Safe End To Pipe-Nozzle Of Nuclear Power Plant

The connecting for safe end and pipe-nozzle of nuclear power plant is the typical dissimilar metal welded joint, which is the weakest link that failure often occurs. To proceed accurate structural integrity assessment and LBB analysis, the constraint effect at the crack tip should be considered. So it is necessary to establish the constraint-dependent J-R curves of dissimilar metal welded joint of the nuclear power plant, In this paper, based on the method combining the finite element model with experiment, the crack-tip constraint parameters of specimens in different locations of dissimilar welded joint or with different geometries were calculated. And different equations of constraint-dependent J-R curves for cracks located in different dissimilar welded joint were obtained. The use of the constraint-dependent J-R curves may increase the accuracy of structural integrity assessment and the analysis of LBB. The main achievements are as follows:(1) The constraint parameter T-stress was modified, and load-independent τ*was obtained. The τ*could be used to characterize the crack-tip constraint level during ductile crack propagation and to construct constraint-dependent J-R curves. The calculation of constraint parameter τ*was much easier than Q.(2) Based on the modified J-τ*theory and the fracture simulation and test results of different SENB specimens, the equation of constraint-dependent J-R curves of homogeneous base metal A508steel was obtained. Moreover, the equation could be used to predict the J-R curves of specimens with different loaded moed(CT, SENT and CCT specimens) accurately.(3) Based on the modified J-τ*theory, constraint-dependent J-R curves of cracks in different location of dissimilar metal welded joint for connecting safe end to pipe-nozzle for nuclear power plant were constructed. The predication of constraint-dependent J-R curves for the weakest area in dissimilar metal welded joint were verified by test and numerical simulation. The results showed that the modified J-τ*theory could be used to construct constraint-dependent J-R curves not only for homogeneous material, but also for dissimilar metal welded joint with obvious strength mismatch(material constraint).(4) According to three-dimensional finite element model, the constraint parameter τ*was used to characterize the crack-tip constraint level for internal circular surface crack of nuclear pipeline and the influence rule of crack depth and crack length on constraint parameter τ*were also obtained. Constraint-dependent J-R curves were used to analyze the LBB behaviour of nuclear pipeline which showed that the LBB assessment without considering the constraint effect would be over conservative.