Synergistic effect study on Cl− and SO42− for 2Cr13 used in a low-pressure cylinder of steam turbines at peaking unit

Purpose The deep peaking of thermal power plants is an inevitable consequence of the development of new energy sources, and this phenomenon leads to considerable alterations in the temperature of the low-pressure cylinder, which in turn exacerbates the corrosion of impurity anions in the specimen. This paper aims to reveal the mechanism of corrosion in low-pressure cylinders. Design/methodology/approach In this study, the corrosion behavior of 2Cr13 steel for the low-pressure cylinder of steam turbines was investigated under different temperatures (60°C, 90°C, 120°C and 150°C) and different ratios of Cl−, SO42− and CH3COO− concentrations (1:1, 1:2, 1:3, 2:1 and 3:1, respectively). Moreover, its specimens were examined by scanning electron microscopy, energy dispersive X-ray spectroscopy and X-ray diffraction. Findings Experimental results showed that the corrosion degree of the specimens increased with the increase of the impurity anion concentration, and the maximum corrosion rate of 0.03819 g/(m2·h) was exhibited at 150°C, even though the total ionic concentration of Cl−:SO42− = 2:1 was less than that of Cl−:SO42− = 3:1; the reason is that SO42− can still compete with Cl− for adsorption at a concentration of Cl−:SO42− = 2:1 at 150°C, thus synergistically promoting the corrosion of the specimen. Originality/value It was found that at 150°C and Cl−:SO42− = 2:1, the interaction of chloride ions and sulfate was synergically promoted. The reason for this was that SO42− was still able to compete with Cl− for adsorption, thereby reoccupying the site occupied by Cl− and enlarging the pitting pit. Therefore, effective measures such as the prompt removal of broken particles of the anode resin should be implemented to prevent corrosion by impurity ions.