Performance of Type 309 SS Overlay in the Lower Furnace of a Black Liquor Recovery Boiler, 2001 Engineering / Finishing & Converting Conference Proceedings

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Type 309 SS overlay was applied by automatic overlay machines on both rear and front walls above the furnace floor below the smelt line, including smelt openings and primary air port openings, at different locations in 1987, 1989 and 1992, respectively, in a black liquor recovery boiler in the Midwest. Both rear and front walls were protected by the weld overlay up to the liquor gun elevation. The overlay applied in 1987, 1989 and 1992 was visually inspected in July 2000. An overlaid waterwall sample was obtained from the 1987 overlaid rear wall for metallurgical evaluation. The metallurgical evaluation included the determination of corrosion attack on the overlay, the integrity of the weld overlay and the substrate steel, and tensile properties of the overlaid waterwall tube after 13 years of service. The overall performance of the 309 SS overlay after services up to 13 years is reported based on the results of the visual examination of the boiler at different locations including primary air port openings and smelt openings, and the metallurgical evaluation of an overlaid waterwall sample. The 309 overlay has provided excellent protection for the lower furnace wall from the floor bed up to the liquor gun elevation, including primary air port openings and smelt openings. The overlay was intact and was in good condition with no sign of mechanical degradation after service for up to 13 years.