448 / 2018-12-29 09:47:16

Corrosion of Turbine Alloys for Supercritical Carbon Dioxide Cycle

supercritical carbon dioxide; corrosion; oxidation; candidate alloys

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The corrosion behavior of turbine materials in supercritical carbon dioxide (S-CO2) was investigated. Compared with the traditional steam-water Rankine cycle system, the supercritical carbon dioxide (S-CO2) Brayton cycle has several potential benefits, such as high efficiency, small equipment size, and low capital cost. Achieving those benefits will depend on overcoming a number of technical, engineering and materials science challenges. Besides the mechanical loads, the turbine components, in the environment of high temperature and high pressure S-CO2, have to withstand oxidation, carburization, and other corrosion. Therefore, it is necessary to study the corrosion behavior of related candidate materials in S-CO2.
In order to be similar to the actual service situation of the material, a corrosion testing device system, with flowing CO2 under high temperature and high pressure, was established. The maximum design parameters of the device can reach 750 癈 / 30 MPa, and will be able to operate steadily over a long period of time. Then the corrosion testing was carried out at 20Mpa pressure at 600 癈 and 700 癈 up to 3Kh. The materials tested are mainly in-service and candidate steam turbine materials, including low-Cr ferritic steels, 9-12% Cr steels, austenitic steels and nickel base alloys. The corrosion rate of samples is determined by weight change measurements. The surface morphology and the composition of the corrosion products will be analyzed by XRD, SEM, EDS and other analytical techniques. The short-term results show that the Low-Cr ferritic steels may not be able to use in high temperature parts of supercritical carbon dioxide turbines due to the severe exfoliation of corrosion product.