Stress corrosion cracking susceptibility of 17-4PH turbine steel in aqueous environments

Abstract

The susceptibility of a 17-4PH type steel to stress corrosion cracking (SCC) in low pressure steam turbine environments was assessed using slow strain rate testing. Environments tested included concentrated solutions of NaCI and NaOH at 90°C. The effects of NaCl solution pH, additions of CuO and CU₂O, and cathodic and anodic polarisation were also investigated. It was concluded that this steel is susceptible to SCC in acidic NaCl solutions, under unpolarised conditions and under anodic or cathodic polarisation. In NaOH solutions, the steel was not susceptible to SCC at cathodic or anodic potentials. Addition of copper oxides to the NaCl and NaOH solutions was not found to promote susceptibility to SCC. It is concluded that both hydrogen embrittlement and anodic dissolution mechanisms are responsible for the SCC susceptibility of the steel tested.