Optimisation of heating and cooling of pressure thick-walled components operating in the saturated steam area

Abstract

The paper presents a new method of determining optimum temperature variations of the fluid during heating and cooling of cylindrical thick-walled components weakened by holes. The temperature of the fluid located or flowing through the pressure component is equal to the saturation temperature.The stress concentration factors at the edges of the holes were determined using the Finite Element Method (FEM) to represent the real construction of the junction between the element and the spigot.Optimum fluid temperature variations were determined so that the maximum equivalent stress at the edge of the opening is equal to the permissible stress determined concerning thermal fatigue. The equivalent stress at the hole edge at the point of its concentration includes thermal stress and stress due to pressure. Optimum temperature changes of hot water and steam-water mixture were determined during heating up and cooling down of the boiler drum, i.e., during boiler start-up and shutdown.Three-dimensional computations of the transient field of temperature and stress were carried out for the junction of the drum and downcomer to show that the equivalent stress at the edge of the hole does not exceed the allowable stress if the optimum temperature of the fluid was estimated by the proposed method.