Hydrogen corrosion is a form of metal corrosion occurring in the presence of anoxic water. Hydrogen corrosion involves a redox reaction that reduces hydrogen ions, forming molecular hydrogen.
Metals enter aqueous solution and are oxidized.
Oxidation reaction (pH independent):
Reduction reaction in acid solution:
In an acidic solution, the water molecules are protonated and the hydronium ions (H3O+) are directly reduced into H2.
Reduction reaction in neutral or slightly alkaline solution:
In a neutral or slightly alkaline solution, the protons of water are reduced into molecular hydrogen giving rise to the production of hydroxide ions responsible of the precipitation of the slightly soluble ferrous hydroxide (Fe(OH)2).
This finally leads to the global reaction of the anaerobic corrosion of iron in water:
Transformation of ferrous hydroxide into magnetite