Corrosion of Candidate Alloys in Superciritical Carbon Dioxide

by Guoping Cao, Mark Anderson, Kumar Sridharan, Lizhen Tan, & Todd Allen
University of Wisconsin, Madison

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Materials corrosion will be an important consideration in the design of a carbon dioxide cooled system, particularly at higher operating temperatures. The corrosion resistance of ferritic steels F91 and HCM12A, ODS ferritic steel PM2000, austenitic alloys 316 stainless steel, 310 stainless steel, 800H, and AL-6XN, and Ni-based alloys Haynes 230, Alloy 625, and PE16 were tested in supercritical carbon dioxide at 650°C and 3000 psi. The tests were performed for exposure durations of 500, 1000, 1500, 2000, and 3000 hours. The corrosion rate of the alloys was determined from weight gain measurements after each exposure time. The surface oxide layer was characterized using x-ray diffraction and scanning electron microscopy equipped with energy dispersive spectroscopy to determine the phases, surface morphology, thickness, and composition of the oxide layers. In general, alloys PM2000, Haynes 230, Alloy 625 and PE16 exhibited excellent corrosion resistance. There was significant spallation of the oxide layer in 316 and 310 stainless steels. The presence of aluminum in PM2000 and PE16 is very effective in imparting excellent corrosion resistance due to the formation of a protective aluminum-oxide layer. PM2000 has 5.5% aluminum and forms a thin and dense aluminum-oxide layer. PE16 contains about 1.1% aluminum. The oxide layer in this alloy consisted of two layers. An outer layer was mainly composed of chromium-oxide and the inner layer was mainly composed of aluminum-oxide. The oxide layer in Haynes 230 and Alloy 625 is mainly composed of chromium-oxide which also provides very good corrosion resistance in supercritical carbon dioxide. Ferritic steels F91 and HCM12A exhibited severe corrosion and spallation. Therefore, they were deemed to be unsuitable for use in the supercritical carbon dioxide test conditions used in the present study.