ABSTRACT
Hydrogen attack is a form of damage that occurs in carbon and low-alloy steels exposed to high-pressure hydrogen gas at high temperatures for extended time. The damage may manifest itself as loss in strength of the alloy or formation of cracks and fissures, and is prevalent at temperatures above 200°C. Under these conditions the reaction occurs between absorbed hydrogen and the iron carbide or the carbon in solution resulting in the formation of a hydrocarbons, generally
The methane produced does not dissolve in iron lattice and internal gas pressures lead to the formation of fissures or cracks. The generated defects or the decarburization itself may lower the strength and ductility of the steel. The decarburization may take place internally or at the surface. In the latter case, the decarburized layer grows to increasing depths as the reaction continues. Cracking may develop in the metal under tensile stress, or the progressive weakening of the metal may result in failure by some other mechanism. The damage is dependent on temperature and hydrogen partial pressures. Surface decarburization takes place at temperatures above 540°C and the internal decarburization at temperatures above 200°C. Hydrogen attack can take several forms within the metal structure depending on the severity of attack, stress, and the presence of inclusions in the steel. In the absence of stress, a component may undergo a general surface attack. The fissures formed are parallel to the metal surface. Areas of high-stress concentration are often the initiation point of hydrogen attack because of preferential diffusion of hydrogen to these areas. Isolated decarburized and fissured areas are often found adjacent to weldments. Blisters and laminations may also result from severe hydrogen attack.
