Alloys were evaluated in the GEGAS 25 ton/day coal gasification pilot plant operating at 300 psig (2.1 MPa gauge). The exposure period lasted for approximately 500 h under gasification conditions. Coupons were exposed in the gasifier (below the bottom grate and in the off-gas) and spray-quench vessel. Ferritic alloy 18Cr-2Mo was the best performing alloy (<20 mpy (0.5 mm/y)) in the air-superheated steam (temperature range: 500/sup 0/ to 1000/sup 0/F (260/sup 0/ to 538/sup 0/C)) environment in the ash pit below the grate assembly. Austenitic alloys Types 304 and 316 underwent stress-corrosion cracking. Irregular corrosion and pitting attack were the modes of corrosion for martenstic alloy Type 410, low-alloy steels 5Cr-0.5Mo and 2.25Cr-1Mo, and carbon steel A515. Their corrosion rates were >100 mpy (2.5 mm/y). In the gasifier off-gas test location, alloys Incoloy 800, Incoloy 825, and 20Cb-3 gave the best corrosion performance in the low-Btu product gas. Alloys 18-18-2, 18Cr-2Mo, and Type 321 experienced corrosion losses due to scaling; intergranular corrosion was experienced by Types 304 and 316. Operating temperatures ranged from 1000/sup 0/ to 1200/sup 0/F (538/sup 0/ to 649/sup 0/C). Process conditions were much milder for alloy coupons in the spray-quench vessel during 500 h exposure. High-alloy steels (18-18-2, 18Cr-2Mo, Types 304 and 316) experienced little corrosion at 350/sup 0/ to 400/sup 0/F (177/sup 0/ to 204/sup 0/C) in the vapor phase. The performances of carbon steel A515 and cast iron A278 were unacceptable since corrosion rates were >30 mpy (0.8 mm/y). 13 refs., 11 figs., 7 tabs.