Effect of chloride and sulfate ions on crevice corrosion behavior of low-pressure steam turbine materials

Crevice corrosion behavior between homogeneous and dissimilar materials of 13Cr and 3.5NiCrMoV steels was investigated in simulated boiler waters containing chloride ions (Cl−) and sulfate ions (SO42−), using open circuit potential (OCP) measurements in addition to morphology analysis. Pitting occurred inside the crevice not only on 13Cr steel but also on 3.5NiCrMoV steel in the test water containing 100 ppm Cl−, while it was suppressed by the coexistence of 50 ppm SO42− in the water with the 100 ppm Cl−. However, the presence of 50 ppm SO42− in the test waters promoted uniform corrosion on 3.5NiCrMoV steel inside the crevice.