A. Marek

Local Stress-Strain Behavior of a High-Temperature Steam Valve Under Transient Mechanical and Thermal Loading

The problem of determining stress-strain characteristics in a selected component operating in a power plant is discussed. Steam valve in transient working conditions during a power unit start-up is taken as an example. The aim of the paper is to prove the possibility to use measurements of steam temperature and the temperature of selected points of the investigated elements for defining boundary conditions of the heat transfer problem as well as to verify operative correctness of the elaborated computer models. The essential importance of time-variable and non-uniform temperature field for the course of local stress changes that results in metal fatigue processes is shown. The method of the computer model validation is discussed as the one of important problems which should be solved if we wanted to predict properly the variable temperature field. The problem of materials behavior under mechanical and thermal loading in the selected component has been discussed.

The Impact of the Heat Transfer Coefficient on High-Temperature Distributions in Steam Valve

The paper attempted to assess the impact of a variable over time heat transfer coefficient on the courses of temperature obtained in the selected areas of the analysed element. The object of the tests was a steam valve. A constant value of this coefficient during such component design is assumed in standards. However, in view of the fact that in devices used in power engineering the state of aggregation of the medium and its flow rate frequently change, the value of the coefficient should be treated as variable. Its value depends on the temperature and pressure. It has been shown that changes in time of the heat transfer coefficient have a strong influence on the temperature distributions in the component.

Research on the Dependence between the Fatigue Life of X20CrMoV12.1 and P91 Steels under the Conditions of the Interactions of Thermo-Mechanical and Isothermal Low-Cycle Fatigue

The paper presents the correlation between fatigue life determined under the conditions of low-cycle fatigue (LCF) and thermo-mechanical fatigue (TMF). Fatigue life values computed using own parameter P and results obtained based on the author’s own research and literature from the publications have been shown. The tests LCF and TMF have been performed for steels used for devices operated in the power engineering industry under the conditions of variable mechanical and thermal interactions X20CrMoV12.1 and P91.