Stress corrosion cracking of A471 turbine disk steels: Effects of dissolved oxygen and carbon dioxide in high-purity water: Final report
Experiments were performed to determine the effect of dilute impurities in high purity water on the rate of initiation and growth of stress corrosion cracks in NiCrMoV steels. 3.5 NiCrMoV steels of commercial quality, high purity, and high purity with intentionally added tramp elements were investigated. Dissolved oxygen and carbon dioxide were the primary water impurities investigated. The tests were conducted on constant load, smooth bar tensile specimens of the NiCrMoV steels in flowing 160C high purity water containing various dilute levels of impurities. It was determined that the initiation rate is very sensitive to changes in dissolved oxygen content; the peak initiation rate are achieved between 20 and 80 ppB dissolved oxygen. The initiation rate is less sensitive to dissolved CO2 content. The crack growth rate in high purity water is only weakly dependent on dissolved O2 and CO2. This work shows that the crack growth rate is strongly dependent on the yield strength (and therefore the microstructure that develops as a result of tempering) of the turbine disc alloy, whereas the initiation rate is only weakly dependent on material yield strength. In addition, crack growth rates decrease as grain sizes are decreased. In general, crack growth rates are very slow (less than 10 m/s) in these dilute environments in materials with yield strengths below 690 Mpa (100 ksi). The results of these experiments indicate that a hydrogen-assisted process may be an important cracking mechanism in these alloys in these dilute environments. Implication of a hydrogen-assisted mechanism could have important consequences in the design and selection of turbine disc alloys.
- Research Organization:
- SRI International, Menlo Park, CA (USA); Electric Power Research Inst., Palo Alto, CA (USA)
- OSTI ID:
- 6440894
- Report Number(s):
- EPRI-NP-5182; ON: TI87920477
- Country of Publication:
- United States
- Language:
- English
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220200* -- Nuclear Reactor Technology-- Components & Accessories
36 MATERIALS SCIENCE
360103 -- Metals & Alloys-- Mechanical Properties
360105 -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
CARBON COMPOUNDS
CARBON DIOXIDE
CARBON OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
CHEMISTRY
CHROMIUM ALLOYS
CHROMIUM STEELS
CHROMIUM-NICKEL STEELS
CORROSION
CRACK PROPAGATION
CRYSTAL STRUCTURE
DESTRUCTIVE TESTING
ELEMENTS
IRON ALLOYS
IRON BASE ALLOYS
MACHINERY
MATERIALS
MATERIALS TESTING
MECHANICAL PROPERTIES
MICROSTRUCTURE
NICKEL ALLOYS
NONMETALS
NUCLEAR FACILITIES
NUCLEAR POWER PLANTS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
POWER PLANTS
REACTOR MATERIALS
STEAM TURBINES
STEELS
STRESS CORROSION
TENSILE PROPERTIES
TESTING
THERMAL POWER PLANTS
TURBINES
TURBOMACHINERY
WATER CHEMISTRY