Alkali sulfates and chlorides may result in rapid corrosion attack of the materials during the process of biomass-fired power generation. The 9-mm-thick 12Cr1MoV superheater tube in biomass-fired boiler was cut into samples by wire cutting. Hot corrosion behaviors of the materials in molten NaCl-50% KCl, KCl-50% K 2 SO 4 , NaCl-50% Na 2 SO 4 , and Na 2 SO 4-50% K 2 SO 4 at 923 K were investigated by the weight change kinetics, scanning electron microscopy, as well as energy-dispersive spectroscopy. The weight gain curve was studied by electronic balance after each experiment cycle at 12, 24, 48, and 60 h. Compared to the microstructures of the corrosion surface and cross section of each material, concentrated pores and cracks were observed on the samples in molten NaCl-KCl, indicating that chlorides induce severest corrosion by active oxidation of chlorine in all cases. There is an extensive decrease in corrosion rates when mixing chlorides and sulfates together, where active oxidation was inhibited by the sulfates. It is interesting to note that sodium (Na) is not as active and detrimental as contents of potassium (K) to the corrosion of 12Cr1MoV steels, which results in the slightest corrosion effects by NaCl-Na 2 SO 4 both on the surface and cross section of the specimens. Therefore, appropriate adjustment on the mixtures of chlorides and sulfates helps to improve the corrosion resistance of 12Cr1MoV.

Biomass energy, as a reliable renewable energy source, has gained more and more attention. However, microstructure degradation and corrosion fatigue damage of heat pipes hinder its further application. In this paper, high temperature corrosion fatigue characteristics of 12Cr1MoV steel under a mixed alkali metal chloride salt environment and mixed sulfate salt environment were investigated. Fatigue tests with different total strain amplitudes were performed. Results show that the effect of total strain amplitude on the cyclic stress response of the alloy is approximately the same under three different deformation conditions. With the increase of the cyclic numbers, the alloyed steel mainly exhibited cyclic hardening during loading. The fatigue properties in air environment were the best, which is most obvious when the total strain amplitude is ±0.3%. The fatigue life of samples in mixed alkali metal salts is the shortest. Furthermore, the fatigue fracture morphology of the alloyed steel in different environments were also deeply analyzed. This experimental study attempts to provide a theoretical reference for solving the problem of rapid failure of heat pipes in biomass boilers, and to establish a scientific basis for the material selection and safety operation.

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