Investigating Fireside Corrosion Behavior and Mechanism of Low-Alloy Water Wall Tube of Ultra-Supercritical Power Plant.

The corrosion thinning behavior and mechanism of low-alloy water wall tubes of an ultra-supercritical power plant was investigated via SEM, EPMA, XRD, TEM, and laboratory simulation experiments. Fireside corrosion was first initiated by chemical potential- and concentration-governed transportation and diffusion, sequentially facilitated by sensitization, which was observed by TEM in terms of the carbide matrix precipitation on the grain boundary, and finally accelerated by the kinetic controlled growth, leading to the final thinning behavior. Laboratory experiments revealed that the reduced atmosphere corrosion kinetic simulation followed the linear law, as well as a different corrosion scale structure layer, compared to the furnace corrosion sample; the reduced atmosphere condition in the laboratory experiment inhibited the oxidation process and layer growth. The frequent shift between the oxidizing and reducing properties of the atmosphere around the water wall tubes during boiler operation may contribute to the delaminated oxidation layer.