Laboratory evaluation of Cr3C2-NiCr spray coatings for water wall tubes of coal firing boiler

Abstract

Long-term stability operation is requested in the boiler for thermal power generation. Recently, thinning in the tube of heat exchanger due to the grooving corrosion has been actualized in the pulverized coal combustion boiler. Corrosion damage with the grooving corrosion was detected in the burner zone and nearby area with high thermal load as a consequence of cyclic thermal stress (localized tube surface temperature fluctuation on account of slag detachment and tube surface temperature fluctuation induced by wall blower operation and other causes) on the furnace side of the tube wall in an atmosphere containing H2, H2S, and O2, which leads to cracking of the corrosion product layer. Thermal spray coatings applied to the surface of boiler components such as heat exchanger tubes are effective as the countermeasure. In this paper, the Cr3C2-NiCr spray coating was performed by the high-velocity oxygen fuel spraying (HVOF) and the atmospheric plasma spraying (APS) . The characteristics of the spray coatings were evaluated by adhesive strength, high temperature hardness, and the abrasive wheel wear test, the high temperature erosion test, and the high temperature corrosion test, etc. The evaluation results proposed the method of evaluating the spray coatings to apply to the coal fired boiler in the laboratory.