Research On Thermal Ratcheting Boundary Of Pressure Pipeline In Nuclear Power Engineering

Thermal ratcheting boundary of pressure pipeline in nuclear power engineering is popular topic to researchers and engineering recently. The requirement for checking the thermal ratcheting boundary was specified by many national codes. However, they are not suitable for the complex loadings and structures due to their limitation. Therefore, it is necessary to improve the existed thermal ratcheting boundaries by analyzing their limitation and applicability. This study has an important theoretical significance for improving the structural design of the nuclear power engineering.According to the state-of-art of thermal ratcheting boundary, the main contexts of this thesis are summarized as below:1. Validation of Bree’s diagram by finite element methodIt is demonstrated that Bree’s diagram can be simulated reasonably by combining the definition of shakedown, the linear relationship between the plastic strain increment and mechanical stress and the method of equivalent plastic strain increment from C-TDF codes.2. Influence factors of the thermal ratcheting boundary(1) The thermal ratcheting boundary simulated by elastic perfectly-plastic model is most conservative and the result by multilinear model is the upper bound. The modified thermal ratcheting boundaries are proposed on the base of Chaboche, multilinear and Abdel-Karim-Ohno models respectively.(2) The influence of wall thickness and ratio of radius to thickness of pressure piping on the thermal ratcheting boundary is very small.(3) The thermal ratcheting boundary is more conservative with a decreasing axial load for thin-walled tubular subjected to cyclic temperature, internal pressure and axial tensile stress. However, the thermal ratcheting boundary is more conservative with an increasing axial compression stress. The modified thermal ratcheting boundary is proposed based on the different axial loads.3. Envelope curves of the thermal ratcheting boundary of transition in pipeThe thermal ratcheting boundary of transition in pipe is investigated on the base of the elastic perfectly-plastic and Abdel-Karim-Ohno models. And then, the envelope curves of the thermal ratcheting boundary are proposed by using Bree’s diagram, which covers different sizes of transition.