The effect of aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels
- Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab.
- Babcock and Wilcox Co., Alliance, OH (United States)
The effect of elevated temperature aqueous environments upon the initiation and propagation of fatigue cracks in low-alloy steels is discussed in terms of the several parameters which influence such behavior. These parameters include water chemistry, impurities within the steels themselves, as well as factors such as the water flow rate, loading waveform and loading rates. Some of these parameters have similar effects upon both crack initiation and propagation, while others exhibit different effects in the two stages of cracking. In the case of environmentally-assisted crack (EAC) growth, the most important impurities within the steel are metallurgical sulfide inclusions which dissolve upon contact with the water. A ``critical`` concentration of sulfide ions at the crack tip can then induce environmentally-assisted cracking which proceeds at significantly increased crack growth rates over those observed in air. The occurrence, or non-occurrence, of EAC is governed by the mass-transport of sulfide ions to and from the crack-tip region, and the mass-transport is discussed in terms of diffusion, ion migration, and convection induced within the crack enclave. Examples are given of convective mass-transport within the crack enclave resulting from external free stream flow. The initiation of fatigue cracks in elevated temperature aqueous environments, as measured by the S-N fatigue lifetimes, is also strongly influenced by the parameters identified above. The influence of sulfide inclusions does not appear to be as strong on the crack initiation process as it is on crack propagation. The oxygen content of the environment appears to be the dominant factor, although loading frequency (strain rate) and temperature are also important factors.
- Research Organization:
- Westinghouse Electric Corp., West Mifflin, PA (United States). Bettis Atomic Power Lab.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC11-93PN38195
- OSTI ID:
- 197144
- Report Number(s):
- WAPD-T-3078; CONF-960389-1; ON: DE96004655; TRN: 96:008265
- Resource Relation:
- Conference: National Association of Corrosion Engineers (NACE) annual corrosion conference and exposition: water and waste water industries, Denver, CO (United States), 24-29 Mar 1996; Other Information: PBD: [1996]
- Country of Publication:
- United States
- Language:
- English
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