Research On Oxidation Experience Of Power Plant Reheater Piping Material For High Temperature Steam Environment

Thermal power is the main way of generating in China. In recent years, with the increasing attention to the environment and energy efficiency issues, developing the supercritical (ultra-supercritical) unit is the most promising direction of thermal power development. However, the requirement of the reheater material performance in supercritical (ultra-supercritical) unit pipeline is very strict, while the oxidation corrosion of materials under such condition jeopardizes the boiler safety as well as the efficiency of the entire plant. Therefore, it is particularly necessary to conduct the research of the oxidation resistance of these materials in power plant.This aritical focuses on the future project of "700 thermal power plant", we conducted the steam oxidation experiments for three types of the most commonly used austenitic stainless steel in reheater, namely, Super304H, TP347HFG, HR3C and a nickel-based alloy Haynes282. The experiments were done in steam environment condition, with the time period of 200,400,600,800 and 1000 hours respectively. The experimental results are evaluated by the aspects of weight gain measurements, surface morphologies observation (SEM), cross-sectional morphology observation cross-sectional morphology observation and elements analysis (SEM-EDS). The results show that Super304H and TP347HFG grow a thick dual-layered structure on the metal surface. The outer layer is porous, Fe-rich and O-rich, as well as Cr-poor and Ni-poor, while the inner layer is compact, Fe-poor and O-poor, Cr-rich and Ni-rich on the contrary. The outer layer is easy-peeling at the high temperature, as a result, the environmental impacts should be restricted. Meanwhile, for HR3C, the oxidation film is thinner, mainly composed by Fe-Cr-Ni oxide, with good compactness and robustness, can be used for the 700 high temperature environment. As for Nickel-based alloy 282, hardly can we find any significant variation during the experiments in the aspects of both oxidation weight thickening and micro-structure within 700 ℃.This thesis analyzes the impact of the three essential factors, namely temperature, Cr and Ni, on the oxidation of the metal material under the condition of high temperature steam environment, and figures out the oxidation resistance of experimental materials under different temperatrue. Meanwhile, the concentration of Cr is essential to the growth of the protective oxidation film. Moreover, the steels mainly composed by Ni, comparing with those mainly composed by Fe, the surface oxidation component NiO has a more stable structure, so that more advantageous under harsh environment.