Methods for controlling or eliminating low-temperature corrosion are continually being sought to improve boiler availability and thermal efficiency. A small pilot plant was constructed at the authors’ company in which factors that affect low-temperature corrosion could be studied under closely controlled conditions. Results of tests on this unit show that: (a) The corrosion rate on carbon steel increases gradually as metal temperature falls below the acid dewpoint, passing through a peak at a metal temperature about 200 F. The corrosion rate then decreases as metal temperature continues to fall but begins to rise rapidly to extremely high values at temperatures just above the water dewpoint (⋍ 120 F). (b) Low-temperature corrosion of carbon steel can be practically eliminated if a method can be found for reducing the sulfur content of oil to about 0.5 percent. (c) The application of low-excess-air operation has the potential of eliminating low-temperature corrosion in boiler plants firing high-sulfur residual oils. (d) Corrosion of carbon steel above approximately 170 F can be reduced 30 percent or more by recirculating 25 percent of the flue gases to the burner. Future work will include a study of the effect of low-excess-air operation on high-temperature oil-ash corrosion and deposition and on the effect of oil ash on low-temperature corrosion.

In the past few years, corrosion of high-temperature superheaters and reheaters has become an increasingly serious problem on coal-fired boilers. A type of corrosion that has occurred on several boilers in the Chicago area which burn high-alkali coal is described. The results obtained from an experimental study of the factors influencing the rate of attack and the control measures applied are described.

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