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Stress Corrosion Cracking


Abstract:
Stress corrosion cracking (SCC) is the formation of brittle cracks in a normally sound material through the simultaneous action of a tensile stress and a corrosive environment
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Stress corrosion cracking (SCC) is the formation of brittle cracks in a normally sound material through the simultaneous action of a tensile stress and a corrosive environment. In most cases, SCC has been associated with the process of active path corrosion (APC) whereby the corrosive attack or anodic dissolution initiates at specific localized sites and is focused along specific paths within the material. In some cases, these are along grain boundaries, in other cases, the path is along specific crystallographic within the grains. Quite often, SCC is strongly affected by alloy composition, the concentration of specific corrodent species, and, to a lesser degree, the stress intensity. In some cases, this latter point may make the use of test methods based on fracture mechanics concepts difficult to utilize effectively due to excessive crack branching and tendencies for nonplanar propagation of cracks.

Furthermore, corrosion film characteristics (i.e., passivation) and local anodic attack (i.e., depassivation) serve as controlling factors in SCC crack initiation and growth. Therefore, localized corrosion can promote SCC making exposure geometry and specimen design important factors. In many cases, mechanical straining or electrochemical inducements such as crevices or controlled potential are utilized to overcome the problems and uncertainties of SCC initiation so that the inherent resistance of the material to SCC can be obtained at reasonable test duration (see Table 1).

Table 1 - Applied Potentials for SCC in Steel Exposed to Various Service Environments
EnvironmentPotential rate (mV, SCE)
Nitrate-250 to +1200
Liquid ammonia-400 to > +1500
Carbonate-650 to -550
Hydroxide-1100 to -850 and +350 to +500

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