해양플랜트 구조물용 고합금강의 고온 부식거동에 관한 연구

Abstract

In this study, we investigate the high-temperature oxidation behavior of four metallic materials S32205, S32750, INCONEL®625, and ASTM A182 F11 through a series of high-temperature thermal exposure tests including heating, isothermal oxidation, cyclic oxidation, and mixed gas oxidation. The goal is to evaluate the applicability of each material to high-temperature oxidizing offshore plant environments. The heating-up and isothermal tests demonstrated that the oxidation resistance of these alloys strongly correlates with their Cr and Ni content. S32205, S32750, and INCONEL®625 exhibited minimal weight gain and formed stable, adherent, and uniform oxide layers even at 900℃. In contrast, F11, with a significantly lower Cr content (~1.5%), showed rapid oxidation, thick oxide scale formation, and poor interface stability, as confirmed by SEM and EDS analyses. Cyclic oxidation testing conducted at 900℃ over five thermal cycles revealed excellent spallation resistance in S32205, S32750, and INCONEL®625. However, F11 exhibited progressive oxide scale delamination and mass loss in later cycles, indicating poor thermal shock resistance and oxide adhesion. In the mixed-gas oxidation test simulating a high-temperature offshore environment (N2+CH4), F11 specimens were exposed to various gas flow rates and holding durations. Regardless of the gas composition, oxidation proceeded under all conditions, with more pronounced degradation observed at longer exposure times. These results indicate that CH4-enriched atmospheres may exacerbate corrosion of low-Cr alloys like F11 in offshore applications. Overall, this study confirms that high Cr and Ni content significantly improves oxidation stability at elevated temperatures. While S32205, S32750, and INCONEL®625 are suitable for primary components in offshore structures, F11 should be limited to secondary applications where direct exposure to oxidizing atmospheres is minimal. These findings offer critical insight into material selection strategies for high-temperature, corrosive marine environments.