Impact of Heat Transfer on Transient Stress Fields in Power Plant Boiler Components

Abstract

In boilers operating in modern power plants, thick-walled elements of complex shapes, such as valves, superheater headers, T-pipes, Y-pipes, four-way pipes, and elbows, are especially prone to fatigue processes. Higher operation parameters and more frequent startups may speed up fatigue damage in these elements. Such damage is a local phenomenon and is caused by thermomechanical fatigue (TMF). This paper presents a method designed for predicting the behavior of components subjected to variable temperature and mechanical loading conditions. This method combines the results of measurements of operating parameters of devices under industrial conditions with those obtained using finite element modeling (FEM). Particular attention was given to the influence of the time-dependent heat transfer coefficient on the local thermomechanical stress–strain behavior of the material. It was stated that heat transfer conditions have a significant impact on local transient stresses and depend on the operation parameters of boilers. Consistency of the temperature changes as a function of time, determined in industrial conditions and calculated on the basis of the model approach, was obtained. This developed and described in the work approach enables defining the conditions of heat transfer on the surface of models of considered components.

Heat Transfer in the Components of Power Boilers and Related Technological and Endurance Problems

“…Long-term exposure to elevated temperatures at constant loads causes processes to creep into them. Simultaneously, changes in working conditions are a potential cause of fatigue phenomena [1][2][3], the impact of which on durability is increasingly being studied.…”

“…These studies include analyses of the operating conditions of individual components of energy equipment, the determination of the fatigue characteristics of materials used for operations at elevated temperatures, and analyses of temperature fields and stresses caused by time-varying loads [4][5][6]. These complementary issues are components of the methodology for assessing the durability of equipment elements, in which the variable temperature field is the cause of time-varying thermal stresses.…”