Fatigue tests have been conducted on Types 304 and 3 16NG stainless steels to evaluate the effects of various material and loading variables, e.g., steel type, strain rate, dissolved oxygen (DO) in water, and strain range, on the fatigue lives of these steels. The results conhn significant decreases in fatigue life in water.Unlike the situation with ferritic steels, environmental effects on Types 304 and 316NG stainless steel are more pronounced in low-DO than in high-DO water. Experimental results have been compared with estimates of fatigue life based on a statistical model. The formation and growth of fatigue cracks in air and water environments are discussed.

Section I11 of the ASME Boiler and Pressure Vessel Code specifies fatigue design curves for structural materials. These curves were based on tests of smooth polished specimens at room temperature in air. The effects of reactor coolant environments are not explicitly addressed by the Code design curves, but recent test data illustrate potentially significant effects of LWR coolant environments on the fatigue resistance of carbon and low-alloy steels. Under certain loading and environmental conditions, fatigue lives of test specimens may be a factor of =70 shorter than in air. Results of fatigue tests that examine the influence of reactor environment on crack initiation and crack growth of carbon and low-alloy steels are presented. Crack lengths as a function of fatigue cycles were determined in air by a surface replication technique, and in water by block loading that leaves marks on the fracture surface. Decreases in fatigue life of low-alloy steels in high-dissolved-oxygen (DO) water are primarily caused by the effects of environment during early stages of fatigue damage, i.e., growth of short cracks lo0 pm, crack growth rates in high-DO water are higher than in air by one order of magnitude. The effects of LWR environments on growth of short cracks are discussed.

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The degradation of fracture toughness, tensile, and Charpy-impact properties of Type 308 stainless steel (SS) pipe welds due to thermal aging has been characterized at room temperature and 290°C. Thermal aging of SS welds results in moderate decreases in Charpy-impact strength and fracture toughness. For the various welds in this study, upper-shelf energy decreased by 50-80 J/cm 2 . The decrease in fracture toughness J-R curve or J IC is relatively small. Thermal aging had little or no effect on the tensile strength of the welds. Fracture properties of SS welds are controlled by the distribution and morphology of second-phase particles. Failure occurs by the formation and growth of microvoids near hard inclusions; such processes are relatively insensitive to thermal aging. The ferrite phase has little or no effect on the fracture properties of the welds. Differences in fracture resistance of the welds arise from differences in the density and size of inclusions. Mechanical-property data from the present study are consistent with results from other investigations. The existing data have been used to establish minimum expected fracture properties for SS welds.

Previous Documents in SeriesEnvironmentally Assisted Cracking in Light Water Reactors Semiannual Report Apd-September 1985, NUREG/CR-4667 Vol. I, ANL-86-31 (June 1986. Reactors Semiannual Report October 1985-March 1986, NUREG/CR-4667 Vol. 11, ANG86-37 (September 1987). Apd-September 1986, NUREG/CR-4667 Vol. 111, ANL-87-37 (September 1987. Environmentally Assisted Cracking in Light Water Environmentally Assisted Cracking i n Light Water Reactors Semiannual Report Environmentally Assisted Cracking in Light Water Reactors Semiannual Report October 1986-March 1987. NUREG/CR-4667 Vol. IV, ANG87-4 1 (December 1987). Apd-September 1987, NUREG/CR-4667 Vol. V, ANL-88-32 (June 1988. October 1987-March 1988, NUREG/CR-4667 Vol. 6, ANG89/10 (August 1989). Apd-September 1988, NUREG/CR-4667 Vol. 7, ANG89/40 (March 1990). Environmentally Assisted Cracking in Light Water Reactors Semiannual Report Environmentally Assisted Cracking in Light Water Reactors Semiannual Report Environmentally Assisted Cracking i n Light Water Reactors Semiannual Report Environmentally Assisted Cracking in AbstractThis report summarizes work performed by Argonne National Laboratory on fatigue and environmentally assisted cracking (EAC) in light water reactors (LWRs) from October 1994 to March 1995. Topics that have been investigated include (a) fatigue of carbon and low-alloy steel used in reactor piping and pressure vessels, (b) EAC of Alloy 600 and 690, and (c) irradiation-assisted stress corrosion cracking (IASCC) of Type 304 SS. Fatigue tests were conducted on ferritic steels in water with several dissolved-oxygen (DO) concentrations to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Tensile properties and microstructures of several heats of Alloy 600 and 690 were characterized for correlation with EAC of the alloys in simulated LWR environments. Effects of DO and electrobhemical potential on susceptibility to intergranular cracking of high-and commercial-purity Type 304 SS specimens from controlblade absorber tubes and a control-blade sheath irradiated in boiling water reactors were determined in slow-strain-rate-tensile tests at 289°C. Microchemical changes in the specimens were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements may contribute to IASCC of these materials. 2.3. 4.5. 6.7.8. 9.10. 11.12.13.14. 15.16. 17. .3 .4 . .6 . .8 . .10 . .12 .13 . Fig. 44(B Executive Summary Fatigue of Fenitic Piping and Pressure Vessel SteelsPlain carbon and low-alloy steels are used extensively in steam supply systems of pressurized and boiling water nuclear reactors (PWRs and BWRs) as piping and pressure vessel materials. Fatigue tests are being conducted on AlOG-Gr B carbon steel and A533-Gr B and A302-Gr B low-alloy steels in water and in air at 288°C to establish the effects of material and loading variables on fatigue life. The results indicate only a marginal effect of lo...