High-temperature corrosion of A210-C carbon steel in simulated coal-combustion atmospheres

Corrosion of A210 C carbon steel was investigated under three different conditions: (1) using synthetic gas mixtures with varying amounts of O₂, SO₂, and HCl; (2) in the flue gas introduced from a coal-fired fluidized-bed combustor (FBC), with and without a deposit cover; and (3) within the freeboard of the FBC firing two different coals. Generally, the oxide scale formed in the temperature range of 370-560°C was mainly Fe₂O₃. The oxidation rate was significantly increased with an increase in temperature. In the synthetic gas mixtures SO₂ and HCl caused scale damage by weakening of the scale-metal interface. The combination of the gases can greatly accelerate the metal corrosion. In the FBC flue gas (condition 2), deposit additions exerted a significant effect on accelerating the metal corrosion. In the FBC freeboard tests (condition 3), the atmospheres containing a higher content of SO₂ and HCl increased the metal corrosion in comparison to corrosion in low-SO₂ and HCl-containing atmospheres. In the former case, an S-enriched phase or pits formed in the residual wastage at or near the metal. This may be the cause of wastage spallation. The HCl effect is discussed but is not conclusive. Moreover, in the FBC system, erosion and deposition appeared to play important roles in exaggerating metal recession.