Stress Corrosion Cracking SCC and SRB

Stress corrosion cracking (SCC) is a type of corrosion that is caused by simultaneous action and effects of both tensile stresses on a vulnerable material in a corrosive medium. 

Gradual formation of biofilms can change chemical concentrations at the surface of metal substrata significantly The physical presence of a biofilm exerts a passive effect in the form of restriction on oxygen diffusion to the metal surface. Active metabolism of the micro-organisms, on the other hand, consumes oxygen and produces metabolites. The net result of biofilm formation is that it usually creates concentration gradients of chemical species across its thickness, which is typically between 10 pm to -400 pm [36]. 

If chlorides are present, the pH of the electrolyte under the biofilm may further decrease, leading to more severe corrosion. When some types of bacteria such as iron-oxidising bacteria (lOB) [32] are present, the tubercule conditions may become very acidic due to combining of the chloride ions with the ferric ions that are produced by the bacteria to form acidic ferric chloride solution inside the tubercule (or biofilm) that is highly corrosive [30]. Pitting is the predominant morphology of MIC [21,46, 104]. 

On the other hand, pitting can act as an SCC initiator because the roots of pits act as stress magnifiers , so that the applied stress becomes multiplied several times, resulting in stresses far in excess of the tensile yield strength, thus producing failure [105]. 

---