Heat-transfer tests were made on tubular specimens of ferritic and austenitic types of superheater alloys which had been exposed to high-temperature steam for periods of 6, 12, or 18 months for the purpose of determining the effect of corrosion by steam. Specimens of scaled tubes and new tubes of the same alloy were machined externally to the same dimensions and surfaces, were mounted in similar heat exchangers, and were tested in series under such conditions that the only difference was in the scaled inner surface of the corroded tube and the bright, smooth, honed inner surface of the clean tube. The heat transfer through ferritic tubes was reduced by as much as fifteen per cent for the temperatures and exposure periods reported upon. The thin, dense scale on the austenitic alloys increased the heat transfer over that of the clean tube by as much as eight per cent, probably because of the increased roughness of the corroded surface.

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