Low-Temperature Corrosion in Flue Gas Waste Heat Recovery: Mechanisms, Materials, and Protection Strategies

Low-temperature corrosion (LTC) caused by acid condensation in flue gas waste heat recovery systems poses a critical challenge to the long-term reliability and efficiency of energy-saving equipment. This study provides systematic analyses of the formation mechanisms of acid condensates, the corrosion behaviors of structural materials, and the corresponding protection strategies under low-temperature acidic environments. The formation and condensation of sulfuric and hydrochloric acids are analyzed in detail, revealing the strong dependence of the acid dew point (ADP) on SO 3 and H 2 O partial pressures. The corrosion mechanisms of carbon steels, stainless steels, and nickel-based alloys are compared, emphasizing the roles of alloying elements (Cr, Mo, Cu, Ni) and the formation of pseudo-passive sulfate or oxide films. Environmental factors such as temperature, acid concentration, dissolved oxygen, and chloride ions are identified as key synergistic variables influencing corrosion kinetics and film stability. On the protection side, recent advances in coating and electrochemical techniques are comprehensively summarized. Ceramic coatings—including single-layer, composite, multi-layer, and self-healing systems—demonstrate excellent chemical inertness and structural adaptability. Polymeric coatings provide cost-effective barrier protection, while metallic coatings, particularly Ni-Cr-Mo- and Cr-based hybrid systems, offer superior thermal and mechanical resistance. Electrochemical methods, including cathodic and anodic protection, are shown to effectively stabilize metal potentials within safe electrochemical regions, providing active corrosion inhibition. Finally, future directions are proposed, emphasizing the integration of micro-anode arrays, self-healing coatings, and intelligent potential control systems to achieve localized and adaptive corrosion protection. This paper thus establishes a comprehensive framework linking corrosion mechanisms, material behavior, and multiscale protection strategies for the design of high-reliability low-temperature heat recovery equipment.