Ratcheting Analysis Of Primary Auxiliary Piping Loop Of Nuclear Power Plants

The ratchetings of piping under internal pressure and bending moment and pressure and torque were evaluated, and ratcheting boundaries have been determined in this study. Also ratcheting of pressurized pipe with pit defect was analyzed. A 3D finite element (FE) model of a Z2CND18.12N stainless steel pipe subjected to load conditions in the operation was simulated via ANSYS software. Four cyclic plasticity models were employed for ratcheting prediction, and their parameters were determined from monotonic tension tests and uniaxial ratcheting tests. The results show that ratcheting prediction of pipe from the four models in decreasing order: Chaboche model, Ohno-Wang II model, Chen-Jiao-Kim model and Bilinear kinematic hardening model. Compared with other load conditions, constant internal pressure and cyclic bending moment or torque can produce larger ratcheting strain of piping. It is found that, for pipe under constant pressure and cyclic bending moment, ratcheting strain in hoop direction is larger than in axial direction, and for pipe under constant bending moment and cyclic pressure, there is larger ratcheting strain in axial direction. Hoop normal strain of pipe under constant pressure and cyclic torque and hoop shear strain of pipe under constant torque and cyclic pressure accumulates more obviously.Ratcheting boundaries of constant pressure pipe under cyclic bending moment and cyclic torque were determined by ratcheting rate control method suggested by C-TDF with the four models. Ohno-Wang II models at different temperature were applied to determine ratcheting boundaries of constant pressure pipe at 25℃, 150℃, 250℃and 350℃. It is found that ratcheting shakedown region decreases with increase of temperature.Ohno-Wang II model was employed to analyze local stress and strain of pipe with pit defects subjected to constant pressure and reversed bending moment. The results show that ratcheting strain level increases with increasing size of radius and depth of pit defect, and that the ratcheting at the pit defect is more sensitive to the depth than with the radius. In addition, with the same radius and position, the ratcheting strain level is higher at an inside pit defect than at an outside pit defect.