Environmentally assisted cracking in light water reactors. Semiannual report, April 1994--September 1994, Volume 19

Abstract

This report summarizes work performed by Argonne National Laboratory (ANL) on fatigue and environmentally assisted cracking (EAC) in light water reactors from April to September 1994. Topics that have been investigated include (a) fatigue of Lbrbon and low-alloy steel used in piping and reactor pressure vessels, (b) EAC of austenitic stainless steels (SSs) and Alloy 600, and (c) irradiation-assisted stress corrosion cracking (IASCC) of q p e 304 SS. Fatigue tests have been conducted on A106-Gr B and A533-Gr B steels in oxygenated water to determine whether a slow strain rate applied during different portions of a tensile-loading cycle are equally effective in decreasing fatigue life. Crack growth data were obtained on fracture-mechanics specimens of S S s and Alloy 600 to investigate EAC in simulated boiling water reactor (BWR) and pressurized water reactor environments at 289°C. The data were compared with predictions from crack growth correlations developed at ANL for S S s in water and from rates in air from Section X I of the ASME Code. Microchemical changes in high-and commercial-purity Type 304 SS specimens from control-blade absorber tubes and a control-blade sheath from operating BWRs were studied by Auger electron spectroscopy and scanning electron microscopy to determine whether trace impurity elements may contribute to IASCC of these materials. . 6. 7.8. 9.10. 11.12. 4. 5.6. 7.8 . 9.10. 11.12. 13.14. Executive Summarv Fatigue of Ferritic 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 A106-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 that in water with high dissolved-oxygen (DO) content, a minimum strain is required for environmentally assisted decrease in fatigue life of these steels, and a slow strain rate applied during the tensile-loading cycle decreases fatigue life more than when applied during the compressive-loading cycle. During the present reporting period, several exploratory tests were conducted on A106-Gr B and A533-Gr B steels in high-DO water in which the slow strain rate was applied during only a portion of the tensile-loading cycle to check whether each portion of the tensile cycle is equally effective in decreasing fatigue life in high-DO water. The results indicate that slow strain rates applied during any portion of the tensile-loading cycle above the threshold strain are equally damaging.The effects of various material and loading variables, e.g., steel type, strain rate, DO, strain range, loading waveform, and surface morphology, on fatigue life of carbon and low-alloy steels in our tests are summarized in this report. Environmentally Assisted Cracking of Alloy 600 and Wrought Stainless Steels in Simulated LWR WaterFr...