Stress-corrosion crack growth rate

Mechanisms of SCC. Crack initiation of EAC is complex and not well understood till now. Most of the SCC systems exhibit short initiation times ranging from minutes to weeks and cracking often occurs due to the change in the environment rather than to a very long initiation time. Stress-corrosion crack growth rates are usually 10 11 and 10-6 m s In systems such as stainless steels in chloride solutions, localized corrosion may create the local conditions prone to crack development, but it is still difficult to explain the initiation of the crack in the absence of localized corrosion in environmental conditions different from that of the crack propagation.95 It should be mentioned that dealloyed surface layers such as certain copper alloys in ammonia-containing solutions are believed to cause SCC.54... 

Fig. 7.104 Effect of stress intensity on stress-corrosion crack growth rate for type 304L stainless steel in aerated MgCI2 at 1 30 °C. Symbols indicate whether propagation occurs as a single or branched crack. Source Ref 165...

Fig. 7.107 Effect of sensitization heattreatmenton stress-corrosion crack-growth rate of type 304 stainless steel in 22% NaCI solution at 105 °C. Sensitized 50 h at 630 °C. Increased chromium depletion at grain boundaries results in increased growth rate and lower threshold K. Source Ref 166...

Fig. 7.113 Dependence of stress-corrosion-crack-growth rate on stress intensity of a high-strength aluminum alloy in several aqueous environments. Crack orientation TL (stress in transverse direction crack propagation in longitudinal direction). Source Ref 159...

S. Yamazaki, Z. Lu, Y. Ito, Y. Takeda, T. Shoji, The effect of prior deformation on stress corrosion cracking growth rates of Alloy 600 materials in a simulated pressurized water reactor primary water, Cotros. Sci. 50 (2008) 835-846. 

R. Magdowski, F. Vaillant, C. Amzallag, M.O. Speidel, Stress corrosion crack growth rates of Alloy 600 in simulated PWR coolant, in Proceedings of the 8th International Symposium on Environmental Degradation ofMaterials in Nuclear Power Systems— Water Reactors, American Nuclear Society, Amelia Island, 1997, pp. 333-338. 

Stress corrosion crack growth rates are usually between 10" and 10 m s . The fastest growth rates are met in systems such as stainless steels in acidic chloride, or copper alloys in concentrated ammonia solutions. Alloy 600 exhibits the slowest crack growth rate, in high temperature water. 

T. Shoji, Z.P. Lu, H. Murakami, Formulating stress corrosion cracking growth rates by combination of crack tip mechanics and crack tip oxidation kinetics, Corros. Sci. 52 (3) (2010) 769-779. 

Krafft [4] and Krafft and Mulherin [5] later extended the TLI model to describe stress corrosion crack growth. Crack growth was viewed in terms of the instability of tensile ligaments where their lateral contraction was augmented by uniform chemical dissolution of the tensile ligaments. For sustained-load crack growth in an inert environment, on the other hand, the reduction in the cross-sectional area of the ligaments would be associated with the creep rate (Landes and Wei [2], Yin et aL... 

Stress corrosion cracking, prevalent where boiling occurs, concentrates corrosion products and impurity chemicals, namely in the deep tubesheet crevices on the hot side of the steam generator and under deposits above the tubesheet. The cracking growth rates increase rapidly at both high and low pH. Either of these environments can exist depending on the type of chemical species present. 

To discover the effective potential ranges for electrochemical protection, the dependence of the relevant corrosion quantities on the potential is ascertained in the laboratory. These include not only weight loss, but also the number and depth of pits, the penetration rate in selective corrosion, and service life as well as crack growth rate in mechanically stressed specimens, etc. Section 2.4 contains a summarized survey of the potential ranges for different systems and types of corrosion. Four groups can be distinguished ... 

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