Strain-induced corrosion cracking

E. Lenz, N. WieHng, Strain-induced corrosion cracking oflow-aHoy steeb in LWR-systems interpretation of susceptibility by means of a three-dimensional (T, 8 dissolved oxygen) diagram, Nucl. Eng. Des. 9 (1986) 331-344. 

H.P. Seifert, S. Ritter, Strain-induced corrosion cracking behavior of low-aUoy steels under boiling water reactor conditions, J. Nucl. Mater. 378 (2008) 312—326. 

In the more recent literature, the term strain-induced corrosion is commonly found, which is a generic term for nonclassical stress corrosion cracking, corrosion fatigue with low cycle frequency, and strain-induced corrosion cracking. For the purposes of a clear distinction between the different types of cracking, this term should be replaced by the definitions below. 

Strain-induced corrosion cracking for corrosion with cracking of materials with protective layers as a result of layer damage on elongation change and corrosion during shutdown periods, nonstationary operation... 

Type of Cracking Stress Corrosion Cracking Corrosion Fatigue Strain-Induced Corrosion Cracking... 

J. Hickling, Strain induced corrosion cracking relationship to stress corrosion crack-ing/corrosion fatigue and importance for nuclear plant service life, 3rd IAEA Specialists Meeting on Subcritical Crack Growth, Moscow, May 1990. 

FIGURE 20.46 Cracking ofprotective layer as a precondition for corrosion fatigue (strain-induced corrosion). 

Caustic embrittlement corrosion (caustic induced, stress corrosion cracking), which occurs as an intergranular form of corrosion where localized stresses and strains are present (and some silicate, which acts as a general corrosion inhibitor that protects grains at the expense of the grain boundaries). 

The most critical conditions are reached in those materials that are subjected to tensile stress that vary in time, such as to induce a slow strain rate and in the presence of notches or sharp flaws. In fact, slow changes in the applied stress, even of modest level, e. g. increases of a few% in the apphed stress during one day or one week, may considerably increase the susceptibihty to stress-corrosion cracking. 

Due to their high sensitivity to strain, temperature variation, vibration, and acoustic waves, embedded extrinsic Fabry-Perot interferometric optical fiber sensors have been developed to detect delamination, based on changes in the acoustic properties of the materials before and after delamination [41]. Impact events and corrosion cracking generate ultrasonic waves, which can be characterized using elliptical core fiber sensors [40]. The in-line Fabry-Perot interferometer seems well suited for the local detection of shear waves and the characterization of impact-induced damage. 

In addition to classic stress corrosion cracking, systems are known in which the static tensile stress is not sufficient to create cracking (e.g., carbonate-bicarbonate solutions). In such cases, critical slow strain rates are necessary to initiate stress corrosion cracking. This type of corrosion is called strain-induced or nonclassical stress corrosion (Diekmann et al. 1983). 

Strain-induced stress corrosion cracking for nonclassical stress corrosion ... 

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