Corrosion of candidate high temperature alloys in supercritical carbon dioxide

Abstract

The corrosion resistance of three candidate alloys is tested in supercritical carb dioxide (S-C0 2 ) at different levels of temperature and pressure for up to 3000 houThe purpose of the testing is to evaluate the compatibility of different engineeri alloys in S-C0 2 for use in a S-C0 2 Brayton cycle. The three alloys used are austeni stainless steel 316, iron-nickel-base superalloy 718, and nickel-base superalloy 7Each alloy is exposed to four combinations of temperature and pressure, consisting of either 550°C or 700°C at either 15 or 25 MPa for up to 1500 hours. At each temperature, an additional sample set is tested for 3000 hours and experienced an increase in pressure from 15 MPa to 25 MPa after 1500 hours of testing. All three alloys are successful in producing a protective oxide layer at the lower temperature of 550°C based on the logarithmic weight gain trends. At the higher temperature of 700°C, 316SS exhibits unfavourable linear weight gain trends at bot pressures of 15 and 25 MPa. In comparison, IN-718 and IN-738 performs similarly in producing a protective oxide layer illustrated through a power weight gain relatio The effect of pressure is most pronounced at the operating temperature of 700° C, where the higher pressure of 25 MPa results in an increased rate of oxide formatio SEM analysis exposes a thin film oxide for both IN-718 and IN-738 but severe intergranular corrosion is exhibited by IN-738. Based on the testing conducted, bo alloys show favourable characteristics for use in S-C0 2 conditions up to 700°C, bu further testing is required to characterize the effect of the intergranular corros ii the stability of oxide in IN-738. 316SS provided favourable results for use in temperatures of 550°C, but the protective oxide deteriorated at an operating temperature of 700°C. m

Review of supercritical carbon dioxide (sCO2) technologies for high-grade waste heat to power conversion

“…The challenge is even emphasized by the high cycle pressures and the strong corrosive behavior that CO 2 shows at temperatures higher than 500 °C. Among the several forms of corrosion, the main relevant mechanisms that can occur in a CO 2 environment are high temperature oxidation, carburization and metal dusting [76].…”

“…a more widespread carburization on the alloy surface, the size of the interstitial carbides increases exponentially until the carbide zone becomes super-saturated and graphite nucleation takes place. As this nucleation begins, the graphite nuclei starts to grow and break the oxide layer previously formed [76].…”

Comparative Maximum Power Density Analysis of a Supercritical Co2 Brayton Power Cycle

“…These studies consist of; thermodynamic cycle models and s-CO2 cycles on commercial or research-based tests [11][12][13][14][15][16]. In addition, studies on the real-time response of s-CO2 power cycles and the development of cycle control strategies [17][18][19], furthermore, research on turbo machines specially designed for s-CO2 flow and on air bearings and seals with turbo machine subcomponents [20][21][22][23], the work consists of studies on high speed electric motor technologies which is essential component for the s-CO2 cycles to be compact [24][25][26][27][28] and material investigations on the interaction of different materials with s-CO2 fluid under high temperature and pressure [29][30][31][32]. Apart from these studies, there is no doubt that one of the parameters that must be taken into consideration is the maximum power density (MPD) when performing cycle optimization.…”