The role of hydrogen in carbonate stress corrosion cracking of low-carbon steel

Hydrogen generation and ingress into low carbon steel has been discovered at high anodic potentials of high-pH stress corrosion cracking in the so-called “standard” carbonate-bicarbonate solution.; The experimental study showed that hydrogen absorption occurs over the whole range of anodic potentials which cause transgranular stress corrosion cracking and coincides with formation of iron (II) carbonate. Also, hydrogen ingress into steel was measured at the lowest part of the range of potentials where most severe intergranular stress corrosion cracking takes place and where the passive film is a composite of siderite and magnetite.; Hydrogen absorption occurs at least 170 mV above the so-called line (a) on the Pourbaix diagram and thus it is not governed by known cathodic reactions but by another process. An adsorption based model for anodic hydrogenation in bicarbonate solution has been proposed. Other experimental findings and theoretical calculations in relation to high pH stress corrosion cracking of low carbon steel are presented.