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Evaluation of exfoliation issues in the fossil-fueled power plant

Popela T., Skoumalová Z., Macák J., Kryková M.

Journal of Achievements in Materials and Manufacturing Engineering

2014

Vol. 64, nr 2

72--77

Purpose: of this work is to evaluate the differences in corrosion behavior and the susceptibility to exfoliation between two steels that are used in fossil-fueled power plants. Design/methodology/approach: The X6CrNiMo17-13-2 and X10CrNiCuNb18-9-3 steels were exposed at supercritical water conditions (600°C, 25 MPa). Behavior of these steels was evaluated and compared. The nature of oxide scales formed on their surface was evaluated by SEM-WDS, XPS, Raman spectroscopy and impedance measurements. Findings: In comparison with the Super 304H steel the 17341 steel showed higher oxidation rate which resulted in higher oxide scale thickness which subsequentially tends to exfoliate more easily. From the microstructural and chemical point of view the oxide scales formed on both steels were very similar. Due to the oxidation kinetics differences the replacement of the 17341 steel by shot-peened Super 304h steel can be advised. However, owing to its high content of carbon, the Super 304H steel is very susceptible to sensitization to intergranular corrosion. Practical implications: The exfoliation phenomenon cannot be fully avoided in the case of austenitic stainless steels. Therefore, the processes carrying out in the power plants need to be carefully monitored in order to prevent the potential system failure. During the service of the fossil-fueled unit the perforation of operations removing the exfoliated oxides is advised. Originality/value: Nowadays in some fossil-fueled power plants where the supercritical regime is introduced the X6CrNiMo17-13-2 austenitic stainless steel suffers severe exfoliation issues. According to the newest trends in material engineering this steel is being currently replaced by shot peened X10CrNiCuNb18-9-3 steel. The value of this work is the evaluation of exfoliation issues of those steels in the fossil-fueled power plant.