Dew Point Corrosion in Thermal Power Systems

Dew point corrosion in thermal power systems arises when acidic vapours or hygroscopic salts in flue gas condense on colder metal surfaces, typically in air preheaters, economisers and ductwork. As flue gas temperature falls below the acid or water vapour dew point, sulphuric acid, hydrochloric acid or chloride-containing salts absorb moisture and form a highly corrosive electrolyte film. This process accelerates pitting and general metal loss, undermining plant efficiency, reducing component life and raising maintenance costs. The phenomenon is particularly pronounced at the cold end of boilers, where temperature gradients encourage deposit formation, condensation of acid vapours and salt deliquescence. Research has demonstrated that fuel composition, boiler load and additives influence the dew point of corrosive species and the characteristics of deposits, while material selection and surface treatments can mitigate damage. Understanding the interplay of thermodynamics, deposit chemistry and metallurgical factors is essential to optimise operational parameters and extend service life of critical power-plant components.

Research from Nature Portfolio

Metallurgical analyses of an early failure in gas heater piping revealed that dew point corrosion dominated the damage mechanism. Investigation of external corrosion on carbon steel pipes operating at low temperatures showed broad, shallow pitting associated with condensed flue gas acids. Microstructural studies identified akaganeite and iron chlorides in corrosion products, while elevated levels of chlorine, nitrogen and sulphur in rust samples confirmed acid dew point attack. The root causes were traced to frequent cold starts, prolonged low-temperature operation and suboptimal alloying levels of Si, Cu, Ni, Cr and Mo. Recommendations emphasised operating above the critical dew point, maximising corrosion-resistant alloy content and adopting better thermal controls to prevent condensation of acidic species.

Dew Point Corrosion in Thermal Power Systems publication trend

The graph below shows the total number of articles in dew point corrosion in thermal power systems across all publications each year (not limited to Nature Index journals).

Technical terms

Dew point temperature: The temperature at which water vapour or acid vapour in flue gas condenses to form liquid on cooler surfaces.

Acid dew point: The specific temperature below which sulphuric or hydrochloric acid vapours condense, creating highly corrosive films.

Hygroscopic salt: A salt that readily absorbs moisture from the environment, often leading to salt deliquescence and corrosion when deposited on metal.

Deliquescence: The process by which a solid salt absorbs sufficient water vapour to dissolve and form an aqueous solution.

Pitting corrosion: A localised form of metal degradation manifesting as small, deep cavities or “pits” on the material surface, often accelerated by acidic condensates.

References

1. Cold-end corrosion caused by hygroscopic ammonium chloride in thermal conversion of biomass and waste. Fuel (2023).
2. A novel methodology for monitoring low-temperature corrosion caused by hygroscopic salts using linear polarization resistance. Electrochimica Acta (2024).
3. Metallurgical investigation of early failure of heater pipes in a gas complex. Scientific Reports (2023).
4. Cold-end corrosion in biomass combustion – Role of calcium chloride in the deposit. Fuel (2023).