Biomass boiler heat‑exchanger tubes suffer serious multi‑source high‑temperature corrosion from alkali salts, water vapor, sulfur‑chlorine species, resulting in tube burst accidents and limiting power‑generation efficiency. This work investigates multi‑source corrosion mechanisms and evaluates laser‑clad Stellite 6 Co‑based protective coatings for TP347H steel.
The dual effect of water vapor, fuel‑condition coupling effect, and competitive regulation of sulfur‑chlorine synergy were clarified. A service‑oriented failure model of Ni‑Al coatings was established, describing γ‑Al₂O₃ destruction by gaseous KCl, aluminate formation, AlCl₃ volatilization and final coating degradation. Dense crack‑free Stellite 6 coatings were prepared by laser cladding. Under 600 ℃ mixed salt‑gas corrosion tests, the Co‑based coating produced compact CoO‑Cr₂O₃ oxide scales and showed superior corrosion resistance compared with bare TP347H. Combined with micro‑characterization and first‑principles calculation, a synergistic protection mechanism of surface oxide barrier and selective intergranular corrosion was proposed.