IMPROVING STRESS CORROSION CRACKING LIFE OF COMPONENTS BY SHOT PEENING

Stress corrosion cracking(SCC) is a progressive fracture mechanism in metals that is caused by the simultaneous interaction of a corrosive agent or "corrodent " and a sustained tensile stress. Structural failures due to SCC is often sudden and unpredictable, occurring after as little as a few hours of exposure, or after months or even years of satisfactory service. It is frequently encountered in the absence of any other obvious kinds of corrosive attack. Virtually all alloy 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 Progressive cracking due to "cyclic " stresses in a corrosive environment is termed "corrosion fatigue". The boundary between SCC and corrosion fatigue is sometimes vague; nevertheless, because the environments that cause them are not the same, the two are treated as separate and distinct metal fracture mechanisms. Compressive residual stresses, such as those induced in the surface layers of a structure by controlled shot peening is often used to prevent or delay both phenomena. It will be presented in this paper the mechanisms of SCC, some Environment-Alloy combinations known to result in SCC, the evaluation of shot peening effects on SCC and varius applications in the industry