The role of hydrogen in microbiologically influenced corrosion and stress corrosion cracking

The phenomenon known as “microbiologically influenced corrosion” (MIC), is very closely related to hydrogen embrittlement of different metallic systems, since microorganims are also a source of hydrogen, by decatalyzing the hydrogen recombination reaction at metal surface, Hads+Hads→H2. On the other hand, “stress corrosion cracking”, (SCC), refers to the synergic action of a specific aggresive environment and the stress condition, which lead to the deterioration or loss of the mechanical properties of a metallic material, linked to the presence of hydrogen. This paper summarizes the role of hydrogen in both phenomena, since the environment supports and justifies the corrosion reactions, being able to change the inside crack chemical conditions, related to the bulk solution. In this way, tensile stresses in SCC, and biological activity in MIC, must be responsible for producing a distribution of embrittlement source, generally hydrogen, with a synergic effect between both phenomena. Certain “metallurgical conditions” of the material with different strength levels associated with diverse values of hydrogen solubility and diffusivity are specially susceptible to MIC and SCC. In addition to this, the principal morphologies of attack and cracking are described.