A field-test was done in a Circulating Fluidized Bed (CFB) boiler burning refuse derived fuel (RDF). The corrosion of alloys ranging from carbon steel (CS) to a nickel based superalloy was tested in panels in the waterwall for 738h. The metal temperatures were kept at about 300°C and 338°C, controlled by separate oil cooling systems. The flue gas composition in the boundary layer at the test panels was on average 27 ppm HCl, 2.6 ppm SO2, 5% O2, 13% CO2 and 2% CO. The corrosion rates were consistently estimated from the weight loss per length unit, and by a profilometry method developed for the test. TP310 (UNS S31008) had the lowest corrosion rates at both temperatures (176 and 284 μm/1000h). The highest corrosion rate at 300°C was 264 μm/1000h for Alloy 625 (UNS N06625). This was due to the pitting corrosion of Alloy 625 that occurred at both temperatures. At 338°C the highest rates were 823μm/1000h for the CS and 400 μm/1000h for TP304L (UNS S30403). Analyzed outer deposits mainly consisted of KCl, NaCl and CaSO4. A layer with mainly potassium oxide was found within the Fe2O3 on CS. For Alloy 28 (UNS N08028) and Alloy 625 a layer of KCl was found in connection to Cr-Ni-Fe oxide.

Subject
Pits, Composition, Corrosion rate, Nickel based alloys, Profilometry, Tubes, Oxide layers, Metal oxides, Waterwalls, Boilers, Potassium chloride, Deposit corrosion, Alloys
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2000
Association for Materials Protection and Performance (AMPP)
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