Affects of applied stresses on the sulfuric acid dewpoint corrosion of 09CrCuSb and 09CuPCrNi

Reducing exhaust temperature is one of the most effective methods to improve the thermal efficiency of industrial boilers. However, the common use of high sulfur content coal makes it impossible on account of the severe sulfuric acid dewpoint corrosion on the heating surface in the rear smoke channel, which is also harmful to boiler operation. In this investigation, tensile stress-sulfuric acid dewpoint corrosion coupling was considered, thus the 09CrCuSb and 09CuPCrNi were applied with tension stress in different concentration of sulfuric acid solution at constant temperature. The effect of tensile stress on passivation of two steels was investigated through measurements of mass changes, corrosion layer morphology and changes of elemental composition. It was observed that applying certain stress at the experimental H₂SO₄ concentration increased the corrosion rate of 09CuPCrNi and 09CrCuSb at 50℃. When applied with stress, the increment of the corrosion rate of 09CuPCrNi specimen was smaller than that of 09CrCuSb in H₂SO₄ solution of low concentration. As the concentration of H₂SO₄ increased, 09CuPCrNi tended to exceed 09CrCuSb. Although the applied stress improved the corrosion layer of 09CuPCrNi in the physical structure, it destroyed the structure of the amorphous material of the inner layer, and the latter was more deadly. As for 09CrCuSb, the application of stress directly aggravated the stripping of the matrix and the corrosion layer, making the internal corrosion layer looser, resulting in the further corrosion to the matrix by O and S elements along the crack, but its effect on the corrosion was limited.