Mechanical and metallurgical considerations on the effects of ppb-level chloride on stress corrosion cracking of low alloy steels in high-temperature water

Abstract

This paper studies the effects of very low-level chloride (< 5 ppb) on the stress corrosion cracking (SCC) growth of low-alloy pressure vessel steel in oxygenated high-temperature water. Chloride levels as low as 3 ppb increase SCC susceptibility. Besides the chemical reason, this paper provides perspectives on the underlying mechanical and metallurgical contributions. A substantial variation was observed from three high-sulphur steels. Sulphur is not the only contributor to SCC. The synergy of material, environmental, and mechanical parameters controlled the crack-tip strain rate and crevice chemistry that govern the SCC response in the high-purity high-temperature water environments at intermediate K.