Compatibility of Different Commercial Alloys in High-Temperature, Supercritical Carbon Dioxide

Abstract

In this work, the compatibility and long-term integrity of candidate structural materials, including the austenitic stainless steel 316NG, the Fe-Ni-based alloy 800H, and the Ni-based alloy 625, were tested in high-temperature and high-pressure SCO2. The exposure time was up to 3000 h. The results showed that the corrosion kinetics approximately followed a near-cubic law for 316NG and 800H. After 3000 h exposure, all oxide layers, mainly composed of Cr2O3, were continuous, compact, and protective, and their thicknesses were about 21~45 nm, 64~88 nm, and 34~43 nm, respectively. In the case of carburization, dark spots corresponding carbon deposition were observed on the surface and a little enriched in the underside of the oxide for 800H. Moreover, the enrichment of trace elements was found at the oxide/substrate interface through GDOES and TEM analyses, i.e., the enrichment of Mn and Si for 316NG, the enrichment of Mn, Si, Al, and Ti for 800H, and the enrichment of Ti and Al for alloy 625.

Review on the Corrosion Behaviour of Nickel-Based Alloys in Supercritical Carbon Dioxide under High Temperature and Pressure

“…As an alloying element, Ti is usually used in most heat-and corrosion-resistant nickel-based alloys and will be oxidized into TiO2 [35,47,48]. TiO2 is mainly formed on the…”

“…As an alloying element, Ti is usually used in most heat-and corrosion-resistant nickelbased alloys and will be oxidized into TiO 2 [35,47,48]. TiO 2 is mainly formed on the surface of nickel-based alloys during high-temperature oxidation with low-oxygen partial pressure conditions [34] in S-CO 2 environments.…”

“…Both of the behaviours mentioned above will lead to the increase of the cation to diffuse along the grain boundary [51]. This behaviour of Ti will finally affect the corrosion resistance of nickel-based alloys both positively and adversely, which will depend on the composition of the alloys and the environments [48].…”

“…As an alloying element, Al usually has a positive effect on the corrosion resistance of nickel-based alloys at high temperatures. Similar to Cr, Al also forms a protective oxide layer [44,48]. The formation of Al 2 O 3 can be promoted by (Cr,Fe) 2 O 3 , which acts as a crystal template [44].…”

“…On the positive side, SI can form a thin and continuous silica film layer [48]. SI will act as a barrier to hinder the C to diffuse into the matrix and form carburized regions.…”