Abstract
Abstract The corrosion behavior of 15CrMo used for water-wall tubes was studied in various urea-containing solution to determine the corrosion problem of water-wall tubes caused by urea in a coal-fired power plant. Urea decomposition tests, together with corrosion experiments, were carried out. The temperature was 320 °C, and the concentrations of urea were 70, 140, 280, 560 and 840 mg/L. Weight loss experiments and surface analysis indicated that the corrosion of 15CrMo steel is mainly manifested as localized corrosion. The corrosion rate of 15CrMo steel increased with the increase of urea concentration, and the maximum value reached 0.686 mm/y (mm per year) when the urea concentration was 840 mg/L. Electrochemical analysis suggested that the corrosion rates of 15CrMo were enhanced substantially by urea decomposition products. The results of UPLC-ESI-MS, infrared spectroscopy and X-ray diffraction showed that urea solution produced corrosive ions NH2COO− during the decomposition process, which caused the corrosion of 15CrMo. Results provided evidence as relevant explanation for the corrosion behavior of 15CrMo in urea solution.
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