Research On Oxidation Corrosion Of Power Plant Metal Materials In Supercritical Water

With the growing energy crisis and environmental problems, our country commit to the development of ultra-supercritical power generation technology, to improve the efficiency of thermal power plant, to reduce the power generation coal consumption and reduce pollutants discharge, to realize clean utilization of coal resources in China. The frequent occurrence of tube rupture is the primary problems in the operation of ultra-supercritical power plant, and seriously affect the supercritical power plant safety. The plan of 700℃ which put forward in 2011 has a higher requirement for the research on oxidation corrosion of power plant metal materials in supercritical water.Investigating the high temperature corrosion experiments through dynamic water cycle on austenitic steel TP347HFG and HR3C at 550,600℃ and 25MPa supercritical water environment, corrosion behavior were studied for experimental period from 200 to 1000 hours, the weight gain, surface morphology and microstructure, XRD and cross-sectional EDS, and element distribution of two materials were analyzed. Weight gain of austenitic TP347HFG is much larger than HR3C. Temperature has obvious influence on TP347HFG oxidation weight, weight gain of TP347HFG at 600 ℃ is about 2-3 times as many as the weight gain of TP347HFG at 550 ℃. While the temperature effect on HR3C oxidation weight increase is not obvious. Both materials have a typical dual oxide layer structure, the outer layer contains loose and porous Fe34 and Fe2O3 oxides, and the inner layer is denser and composed of Fe-Cr-Ni oxide.Under the condition of 550/600 癈,25MPa supercritical steam both the austenitic steel HR3C and TP347HFG have a good oxidation resistance. Because the austenitic steel contains more Cr element, it can form a protective layer of Cr2O3.The Cr element content of HR3C is higher than TP347HFG, so HR3C is more likely to form a continuous dense Cr2O3 layer to improve the metal oxidation resistance. Therefore HR3C have a better oxidation resistance than TP347HFG.In the process of supercritical water oxidation, Cr2O3 in Cr2O3(OH)2 form evaporation, reduce Cr content of metal and density of the Cr oxide layer is damaged. The evaporation rate of Cr is affected by temperature, pressure, gas flow rate and steam chemical properties. Calculated Cr evaporation under this experimental condition, found that Cr evaporation cause the half of the difference between of the calculated value and the actual value of the oxidation weight. The mechanism study of the growth of film hole between inner and outer oxide shows that, the growth of film hole between inner and outer oxide in TP347HFG is influenced by the evaporation of Cr and the ion diffusion of Fe, while the growth of film hole between inner and outer oxide in HR3C is mainly influenced by the evaporation of Cr.