95/04027 The relative erosion-corrosion resistance of commercial thermal sprayed coatings in a simulated circulating fluidized bed combustor environment

Abstract

Bed ash and fly ash samples were retrieved from operating circulating fluidized bed combustor (CFBC) boilers firing three different fuels: anthracite culm, bituminous coal, and biomass. Using these materials, the relative erosion-corrosion resistance of three commercially available thermal sprayed coatings and one weld overlay specimen was determined in an elevated temperature erosion tester. Erosion test conditions attempted to simulate the erosive conditions found at the refractory/bare-tube interface on the combustor waterwall and in the convection pass of the superheater tube banks of a CFBC. The coatings included DenSys DS-200 (a proprietary HVOF Cr{sub 3}C{sub 2}-NiCr cermet coating), Rokide C (a flame-sprayed Cr{sub 2}O{sub 3}-6SiO{sub 2}-4Al{sub 2}O{sub 3} ceramic coating) and Armacor M (an arc-sprayed FeCrSiB metallic coating). The weld overlay was Smooth arc 250 onto low carbon steel. Erosion test results were compared to erosion test results for AISI 1018 and ASTM SA213-T22 steel specimens. The results indicated that the DS-200 coating had the highest erosion-corrosion resistance among the target materials due to its compactness, high density, fine grain structure and a homogeneous distribution of the skeletal network of hard carbides/oxides within a ductile and corrosion-resistant metallic binder.