Corrosion of Thermowells in a Coastal Fluidized Bed Biomass Power Boiler

Abstract A metallographic examination was conducted on a set of degraded alloy thermowells, which were installed in the fluidized bed of a coastal fluidized bed biomass (waste-wood) power boiler. Because of the importance of temperature measurement in the boiler control strategy, the plant wanted to understand the corrosion mechanism and choose longer-lived materials. The analytical results suggest that the corrosion was caused by contact with a molten chloride-containing salt. The relative corrosion resistance ranking order of Alloy 600 > Alloy 625 > Type 310H stainless steel > Type 446 stainless steel is consistent with the reported influence of nickel and chromium alloying on corrosion resistance in molten chloride-containing salts.