This paper presents the results of experiments to determine which variables have the most effect on environmentally assisted cracking (EAC) of reactor pressure vessel steels. Four heats of SA508 and three heats of SA533 were studied in 288°C pressurized water reactor, light water reactor, and boiling water reactor environments. The sulfur content of these materials ranged from 0.004 to 0.025%. The most important variable was found to be the sulfur content and sulfur morphology of the material. A material with a bulk sulfur content greater than 0.010% may be susceptible to EAC. The loading frequency was found to be an important variable. Minor effects of EAC were attributed to the load ratio, ΔK level, and oxygen content of the environment. An experimental method to introduce sulfur directly to the crack tip is described. A time-based method of data interpretation is discussed.
During normal operation light water reactor (LWR) pressure vessels are subjected to a variety of transients resulting in time varying stresses. Consequently, fatigue and environmentally assisted fatigue are growth mechanisms relevant to flaws in these pressure vessels. In order to provide a better understanding of the resistance of nuclear pressure vessel steels to flaw growth process, a series of fracture mechanics experiments were conducted to generate data on the rate of cyclic crack growth in SA508-2 and SA533B-1 steels in simulated 550°F Boiling Water Reactor (BWR) and 550°F Pressurized Water Reactor (PWR) environments. Areas investigated over the course of the test program included the effects of loading frequency and R ratio (Kmin/Kmax) on crack growth rate as a function of the stress intensity factor (ΔK) range. In addition, the effect of sulfur content of the test material on the cyclic crack growth rate was studied. Cyclic crack growth rates were found to be controlled by ΔK, R ratio, and loading frequency. The sulfur impurity content of the reactor pressure vessel steels studied had a significant effect on the cyclic crack growth rates. The Higher growth rates were always associated with materials of higher sulfur content. For a given level of sulfur, growth rates were higher in a 550°F simulated BWR environment than in a 550°F simulated PWR environment. In both environments cyclic crack growth rates were a strong function of the loading frequency. Further, the loading frequency at which the highest cyclic crack growth rate was observed was found to be a function of the applied ΔK level. In most cases, all cyclic crack growth rates were on or under the ASME Section XI high R water reference flaw growth line and above the Section XI air reference flaw growth line, supporting the position of these lines on the growth rate–ΔK level graph.
The results of a study conducted over a number of years to characterize the elastic-plastic fracture properties of submerged arc weld metal are presented in this paper. The fracture properties of four different weldments were investigated at temperatures ranging from 24 to 288°C (75 to 550°F). Tests were conducted using both the conventional multiple-specimen JIc procedure as well as an automated single-specimen unloading compliance technique capable of generating the material JI-R curve.
Test results obtained using the two different procedures are compared. The comparison indicates that while both test techniques generate comparable J-Δa data for a given test condition, JIc values from the respective sets of data can differ. This is attributed largely to the sparsity of data generated by the multiple-specimen technique and the nonlinearity of the JI-R curves as revealed by the single-specimen technique.
Welding procedure was found to have a significant effect on measured toughness. A wide range of fracture behavior was observed. The welding parameters responsible for the observed behavior are discussed. The applicability of the current JIc and JI-R curve test procedures over the wide range of crack growth behavior observed is discussed.
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