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Abstract
The 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 for testing in utility boilers. The probes were designed to maintain metal temperatures using multiple zones, ranging from 650 to 870°C. Three utility boilers, equipped with low NOx burners, were identified that have adequate flue gas temperatures and represent each of the three coal types. New fireside corrosion probe results are presented for mid-western and western coal types, after approximately one year of exposure in the field. Visual examination of samples from the mid-western utility site indicated minimal evidence of significant wall loss for any of the tested materials. Samples removed from the western utility site indicated evidence of wall loss for some tested materials. Further evaluation and quantification of total metal wastage through wall thickness measurements and metallographic examination of subsurface penetration is being undertaken.