As part of the Boiler Materials for Ultrasupercritical Coal Power Plants program, sponsored by the United States (U.S.) Department of Energy (DOE) and the Ohio Coal Development Office (OCDO), the steamside oxidation and oxide exfoliation behavior of candidate alloys have been thoroughly evaluated in steam at temperatures between 620°C and 800°C (1148°F and 1472°F) for times up to 10,000 hours. The results from this test program indicate that the oxidation rates and oxide morphologies associated with steamside oxidation are a strong function of the crystallographic lattice structure and the chromium content of the material. Oxide exfoliation correlates to oxide thickness. The time required to reach the critical oxide thickness for exfoliation can be estimated based on oxidation kinetic relationships. For austenitic stainless steels, shot peening is effective in reducing steamside oxidation/exfoliation, but the efficacy of this technique is limited by the operating temperature. Nickel-based alloys exhibit very low oxidation/exfoliation rates, but have a propensity to form aluminum/titanium oxides along near surface grain boundaries.

In the “Boiler Materials for Ultrasupercritical Coal Power Plants” program, sponsored by the U.S. Department of Energy and the Ohio Coal Development Office, various materials are being assessed for their suitability in the high-temperature, high-pressure environment of advanced ultrasupercritical (A-USC) boilers. Beyond mechanical properties and fireside corrosion resistance, these materials must also exhibit adequate steamside oxidation and exfoliation resistance. A comprehensive database of steamside oxidation test results at temperatures relevant to A-USC conditions has been compiled over recent years. These tests have been conducted on ferritic and austenitic materials with chromium content ranging from 2 to 26%. The specimens were evaluated for oxidation kinetics and oxide morphology. The findings indicate that steamside oxidation behavior is significantly affected by temperature, the chromium content of the material, and the ability of chromium to diffuse through the material's crystallographic lattice structure. Additionally, surface treatments have been applied to enhance the steamside oxidation resistance of certain materials. While these treatments have shown potential, their effectiveness can be limited by the operational temperatures.

A collaborative program by the U.S. Department of Energy and Ohio Coal Development Office aims to identify new materials for ultrasupercritical (USC) coal power plants operating at significantly higher efficiencies. These USC plants require advanced ferritic alloys, austenitic steels, and nickel-based alloys with superior steamside oxidation resistance at high temperatures (up to 800°C). Initial tests on over 20 candidate materials exposed to flowing steam at 650°C for 4,000 hours show promise for nickel-based and austenitic alloys, while highlighting the dependence of oxidation resistance on chromium content for ferritic alloys. Notably, even within 9% Cr ferritic steels, varying compositions resulted in significantly different oxidation behaviors.