“…In both cases, therefore, crack propagation is expected to occur normal to the loading direction and along the rolling direction. Results of crack growth testing have been reported previously, producing crack growth rates for 20% cold work of ~2x10 -11 m s -1 on several specimens at a stress intensity factor (K) of 30MPa√m [7] 1 .…”
Section: Methodsmentioning
confidence: 57%
“…Laboratory studies on austenitic stainless steels in PWR primary coolant environments have shown that propagation of an existing crack by stress corrosion cracking can occur if the material has been subjected to cold work to a level of about 15% or greater [6,7,8,9]. Crack growth rates can be high under some conditions, with rates of several millimetres per year having been measured for 20% cold work and loading normal to the cold working direction [7]. Despite these observations from crack growth tests, the good plant experience of stainless steels exposed to primary coolant suggests that crack initiation is difficult under plant loading conditions [10].…”
Although service experience of austenitic stainless steels exposed to PWR primary coolant has been good, stress corrosion crack propagation has been observed in laboratory tests in the presence of 15% cold work. Data on crack initiation are much more limited and this study therefore aims to improve the understanding of the conditions under which crack initiation and subsequent development of stress corrosion cracking might be possible. Testing was performed on two heats of Type 304/304L stainless steel under slow strain rate tensile loading. A range of analytical techniques were used to characterize the resultant precursor features and cracking, and digital image correlation before and after testing was also used to evaluation the influence of localized deformation on SCC. The results indicate that crack initiation can occur in austenitic stainless steels exposed to good quality primary coolant under dynamic straining conditions; additional testing underway under more plant-representative conditions will be reported later. Significant influences of steel microstructure on crack initiation susceptibility were observed.
“…In both cases, therefore, crack propagation is expected to occur normal to the loading direction and along the rolling direction. Results of crack growth testing have been reported previously, producing crack growth rates for 20% cold work of ~2x10 -11 m s -1 on several specimens at a stress intensity factor (K) of 30MPa√m [7] 1 .…”
Section: Methodsmentioning
confidence: 57%
“…Laboratory studies on austenitic stainless steels in PWR primary coolant environments have shown that propagation of an existing crack by stress corrosion cracking can occur if the material has been subjected to cold work to a level of about 15% or greater [6,7,8,9]. Crack growth rates can be high under some conditions, with rates of several millimetres per year having been measured for 20% cold work and loading normal to the cold working direction [7]. Despite these observations from crack growth tests, the good plant experience of stainless steels exposed to primary coolant suggests that crack initiation is difficult under plant loading conditions [10].…”
Although service experience of austenitic stainless steels exposed to PWR primary coolant has been good, stress corrosion crack propagation has been observed in laboratory tests in the presence of 15% cold work. Data on crack initiation are much more limited and this study therefore aims to improve the understanding of the conditions under which crack initiation and subsequent development of stress corrosion cracking might be possible. Testing was performed on two heats of Type 304/304L stainless steel under slow strain rate tensile loading. A range of analytical techniques were used to characterize the resultant precursor features and cracking, and digital image correlation before and after testing was also used to evaluation the influence of localized deformation on SCC. The results indicate that crack initiation can occur in austenitic stainless steels exposed to good quality primary coolant under dynamic straining conditions; additional testing underway under more plant-representative conditions will be reported later. Significant influences of steel microstructure on crack initiation susceptibility were observed.
“…which show the crack growth rates of specimens tested parallel (S-L), transverse (T-L) and orthogonal (L-S) to the original cold-work direction. In this study, the S-L orientation, in which crack growth is parallel to the cold-working direction produces the greatest susceptibility to SCC and the L-S orientation (crack propagation orthogonal to cold work) the least [20]. Crack propagation in the S-L direction is relatively uniform, whereas, for the T-L orientation, crack propagation frequently appears as fingers of IG cracking ahead of the main crack front, with secondary IG cracking perpendicular to the main fracture surface, Figure 9 [20,21].…”
Section: Stress Corrosion Crackingmentioning
confidence: 99%
“…In this study, the S-L orientation, in which crack growth is parallel to the cold-working direction produces the greatest susceptibility to SCC and the L-S orientation (crack propagation orthogonal to cold work) the least [20]. Crack propagation in the S-L direction is relatively uniform, whereas, for the T-L orientation, crack propagation frequently appears as fingers of IG cracking ahead of the main crack front, with secondary IG cracking perpendicular to the main fracture surface, Figure 9 [20,21]. Figure 8 Crack growth rate of 20% cold-rolled stainless steel, in different orientations, as shown in right (UDR = unidirectional rolling, BDR = bidirectional rolling).…”
Section: Stress Corrosion Crackingmentioning
confidence: 99%
“… Figure 8 Crack growth rate of 20% cold-rolled stainless steel, in different orientations, as shown in right (UDR = unidirectional rolling, BDR = bidirectional rolling). All specimens 0.001% sulphur except R581 and R583 (0.004%) [20]. Figure 9 Optical images of fracture surfaces of S-L specimen (a) and T-L specimen (b).…”
Environmentally assisted cracking (EAC) is a potential threat to the safety and integrity of water-wetted components in operating water-cooled nuclear power plants. Two forms of EAC are commonly distinguished, depending on the form of loading contributing to damage: stress corrosion cracking (SCC) and corrosion fatigue. A number of instances of in-service degradation due to EAC have occurred in operating plants worldwide, often leading to unplanned plant outages. Understanding the causes of EAC is essential to minimise the loss of plant availability due to its occurrence and to avoid the possibility of catastrophic failure, for example, if a crack grew to a critical size in a major pressure boundary component. This paper will describe some examples of these phenomena in the main materials of construction of pressure boundary and other critical components in pressurised and boiling water reactors (BWRs). Over the last several decades, substantial research programmes have been carried out in a number of laboratories worldwide, aimed at further understanding of the processes leading to EAC to manage occurrences in plant and minimise future failures. Selected areas of research on EAC in light water reactor environments are discussed. Corrosion fatigue in low-alloy pressure vessel steels was the subject of considerable attention in the 1980s and early 1990s because of its potential threat to pressure vessel integrity and the publication of data, suggesting that there is a major influence of environment on fatigue crack growth in some laboratory tests. The author's research provided insight into the conditions under which the major environmental effects occur and contributed to the development of an ASME Code Case for pressurised water reactor (PWR) conditions which provided a means of screening based on steel sulphur content and loading conditions. More recently, the research focus in this area has moved to austenitic stainless steels, again providing support to Code Case development and furthering mechanistic understanding. A recent review of knowledge gaps for EPRI provides a basis for future research on environmentally assisted fatigue and will inform the development of new assessment methodologies. A key area of the current study concerns differences in loading conditions between specimens in laboratory tests and plant components subject to transient loading. In the case of SCC, stainless steels have shown the greatest propensity to cracking in BWRs, while Alloy 600 has been a major cause of in-service failures in PWRs, both on the primary side, as recognised by Coriou in the early 1960s, and in secondary environments where a number of different corrosionrelated failure processes have been identified. High-strength alloys, such as Alloy X-750 used for fastener applications, have also caused failures in both reactor types. For austenitic materials, SCC susceptibility is enhanced by irradiation, resulting in failures in core internals components. Ferritic stainless steels also undergo SCC under some specific circums...
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