With the trend towards increasing the energy efficiency of black liquor recovery boilers in North
America, there is a need to utilize superheater tubes with increased corrosion resistance that will permit
operation at higher temperatures and pressures. In an effort to identify alloys with improved corrosion
resistance under more harsh operating conditions, a field exposure was conducted that involved the
insertion of an air-cooled probe, containing six candidate alloys, into the superheater section of an
operating recovery boiler. A metallographic examination, complete with corrosion scale
characterization using electron microprobe spectroscopy, was conducted after a 1,000 hour exposure
period. Based on the results, a ranking of alloys based on corrosion performance was obtained.
Keywords: recovery boiler, black liquor, superheater, tube, corrosion, molten salt, chloride, sulfate, alloy