The effect of potential on the high-temperature fatigue crack growth response of low alloy steels, part 2: sulfide–potential interaction

Abstract

Environmentally assisted cracking (EAC) of low-alloy steels exposed to high temperature dehydrogenated water was found to be dependent on externally applied potential. EAC became active when the specimen was polarized anodically above a critical potential, which was not a function of steels sulfur. However, the plateau crack propagation rate was determined to be dependent on both overpotential and steels sulfur concentration. Hydrogen additions inhibited the ability of applied potential to activate EAC. The behavior was related to the formation of hydrogen ions on the specimen surface through hydrogen oxidation during anodic polarization. A mechanism based on the formation of hydrogen sulfide at the crack tip and hydrogen ions at the crack mouth is presented to describe the process by which sulfides and hydrogen ions affect the critical sulfide concentration at the crack tip needed to establish EAC.