AbstractThe fireside corrosion resistance of candidate materials for the waterwalls and superheater/reheater sections of ultrasupercritical coal fired boilers have been evaluated through field testing as part of a programme cosponsored by the US Department of Energy and the Ohio Coal Development Office. The materials tested include high strength ferritic steels (SAVE12, P92, HCM12A), austenitic stainless steels (Super304H, 347HFG, HR3C), and high nickel alloys (Haynes 230, CCA617, INCONEL 740, HR6W). Protective coatings (weld overlays, diffusion coatings, laser claddings) that may be required to mitigate corrosion were also evaluated. The trials were based on previous laboratory evaluations under synthesised coal ash and flue gas conditions typical of three North American coals at temperatures ranging from 455 to 595°C for waterwall materials, while superheat/reheat materials were tested at 650–870°C. Promising materials from the laboratory tests were assembled on air cooled, retractable corrosion probes ...