Failure analysis and degradation mechanisms of GX130CrSi29 grate bars in a biomass-fired furnace: An industrial case study

Premature degradation of grate bars is a persistent operational challenge in biomass-fired furnaces, particularly when alkali-rich fuels are used, leading to increased maintenance and unplanned outages. Although biomass combustion and ash chemistry have been widely investigated, detailed failure analyses based on service-exposed grate components from operating power plants remain relatively limited. This study investigates the degradation behavior of GX130CrSi29 grate bars retrieved from a 9.9 MW rubberwood-fired reciprocating grate furnace. Failed components collected during scheduled maintenance were examined using a practical failure-analysis approach combining macroscopic inspection with cross-sectional field-emission scanning electron microscopy and energy-dispersive X-ray spectroscopy (FE-SEM/EDS), including elemental mapping and line-scan analysis. The results reveal a reproducible multilayer degradation architecture consisting of (i) an outer adhesion layer enriched in K-, Ca-, and Si-bearing ash deposits, (ii) a porous iron-rich oxide scale, and (iii) a chromium-depleted substrate exhibiting internal oxidation. Elemental distributions show pronounced chromium depletion near the oxide–metal interface together with chlorine- and alkali-bearing deposits. These microstructural and chemical features are consistent with degradation involving chlorine-assisted active oxidation and alkali–silicate-related fluxing under biomass combustion conditions. The position-dependent and non-uniform section loss observed in the grate bars is interpreted using a coupled thermochemical corrosion and flow-assisted removal framework, in which corrosion-weakened oxide and deposit layers may be intermittently detached under localized gas-flow interaction and high thermal loading. Although conceptual rather than predictive, this framework provides a physically consistent interpretation of the irregular degradation patterns observed in service. The findings highlight the dominant role of biomass ash chemistry and furnace operating conditions in controlling grate degradation and provide practical insights for grate material selection and operational strategies in biomass-fired power systems.