Stress Corrosion Cracking Characterization of 3.5 NiCrMoV Low Pressure Turbine Rotor Steels in NaOH and NaCl Solutions

Abstract

Abstract This paper describes a research program conducted to determine susceptibility of steels used in low pressure (LP) turbine rotors of power plants to stress corrosion cracking (SCC) in LP turbine environments. Slow strain rate SCC tests were conducted on samples from two 3.5 NiCrMoV rotor forgings over a temperature range of 38 to 204 C (100 to 400 F). Environments employed included pure NaOH solutions, 3.5% NaCl, pure water, and mixtures of NaOH and NaCl, Na2S, Na2SO4, or CuO. Supplementary electrochemical data also were generated. Test results indicate that the minimum NaOH concentration required to produce detectable SCC decreases with increasing temperature. Addition of small amounts of NaCl reduced the concentration of NaOH necessary to produce SCC at 157 C (315 F). Pure 3.5% NaCl induced SCC at 121 C (250 F). SCC was not detected in either steel in tests in pure water at 157 C (315 F).