Research On The Influence Of Steam-Side Oxide Scale Thickness On Temperature And Stress Distribution Of High-Temperature Boiler Tubes

With the continuous development of the economy, newly-built units gradually orient to large capacity and high parameters. The using of high parameters puts forward higher demand for the metal materials of the tubes, as higher allowable temperature and oxidation resistance temperature are required. With the increase of the operating temperature, the steam side oxidation of the high-temperature boiler tubes has been paid much more attention. In this paper, the affection of steam-side oxide scales on the temperature and stress distribution of the high-Temperature boiler tube is discussed, hoping to obtain reasonable suggestions for the pipe design and boiler operating.Numerical model of high-temperature boiler tube with oxide scales inside is built and the heat transfer process of each part is analyzed in detail. Since the physical parameters of the heat transfer mediums under different temperatures are calculated, the heat transfer boundary conditions of the inner and outer wall under different given operating conditions are determined via the empirical formulae. The heat transfer process on the high temperature convective heating surface is calculated with ANSYS finite element method. The impact of the steam-side oxide scale thickness on the temperature variation patterns of the external surface, the scale/metal interface and the scale/steam interface under various geometries of tubes, steam flows, steam pressures, steam temperatures and flue gas temperatures is obtained. Then the thermal-stress coupled field of the tube is analyzed and calculated in order to get the temperature and stress responses to the steam temperature and flue gas temperature perturbation.The heat transfer property of the tube is affected greatly by the oxide scale, moreover, with the increment of the oxide scale thickness, the thermal stress is larger as the substrate thickness becomes thinner. The effect of steam flow variation is the most biggest among all the factors that affect the wall temperature. Therefore, it shouled be specially monitored during operating. The influence of the tube diameter mainly manifests in the tube thickness. Thicker tubes lead to higher wall temperatures. The influence of temperature perturbation on tube temperature and Von Mises stress is larger than that of the flue temperature perturbation. Thus, choosing of the tube diameter is advised to be based on comprehensive consideration of the safety of both temperature and stress, then the security of the boiler will be advanced.