Caustic Stress Corrosion Cracking in Carbon Steels: Mechanisms, Operating Windows, and Control Strategies in Boilers and Refineries

Caustic stress corrosion cracking (caustic SCC, historically termed caustic embrittlement) remains a high-consequence degradation mode for carbon steel pressure components in boilers and refineries when three conditions align: a locally concentrated alkaline electrolyte, a sustained tensile stress field, and a susceptible microstructure or surface state created by fabrication, welding, aging, or service exposure. This review adopts a mechanism-first framework that links electrochemical and mass-transport conditions produced by caustic concentration (under deposits, in crevices, and in boiling or heat-flux hotspots) to crack-tip processes that govern initiation and propagation. Anodic dissolution bursts driven by protective film instability and localized chemistry are treated as the baseline pathway, while hydrogen uptake is addressed as a conditional contributor that becomes important under sufficiently cathodic potentials and appropriate transport conditions. Recent peer-reviewed studies (2021-2025) are integrated to strengthen the mechanism-first claim, and quantitative anchors for pH and temperature are provided to support an operating-window approach. Finally, a hierarchy of controls and specific non-destructive examination techniques (WFMT, PAUT, TOFD) is mapped to practical integrity management.