Stress corrosion cracking (SCC) is the growth of crack formation in a corrosive environment. It is a progressive fracture mechanism in susceptible metals that is a result of the interaction of a corrodent and a sustained tensile stress. Structural failure due to SCC is often sudden and unpredictable, occurring after as little as a few hours of exposure, or months to years of service. Metal components frequently experience SCC in the absence of any other obvious kinds of corrosive attack. Many alloys systems are susceptible to SCC by a specific corrodent under a specific set of conditions.
The tensile stresses necessary for SCC are “static”, and they may be residual and/or applied (see chart below). It is important to note that all 3 sides of the SCC triangle must be present for SCC to occur. Shot peening eliminates the tensile stress portion of the triangle which prevents SCC from occurring.