Correlations Between Charpy V-Notch Impact Energy and Fracture Toughness of Nuclear Reactor Pressure Vessel (RPV) Steels

Abstract

Both Charpy V-notch (CVN) impact energy and fracture toughness are parameters reflecting toughness of the material. Charpy tests are however easy to perform compared to standard fracture toughness tests, especially when the material is irradiated and quantity is limited. Correlations between the two parameters are therefore of great significance, especially for reactor pressure vessel (RPV) structural integrity assessment. In this paper, correlations between CVN impact energy and fracture toughness of three commonly used RPV steels, namely Chinese A508-3 steel, USA A533B steel, Euro 20MnMoNi55 steel, are investigated with two methods. One method applies a direct conversion using empirical formulas and the other adopts the Master Curve method. It is found that when the empirical formula is used, the difference between the predicted fracture toughness (from the CVN impact energy) and actual test data is relatively small in upper shelf, lower shelf and the bottom of transition region, while relatively large in other parts of the transition region. When the Master Curve method is adopted, whether the reference temperature T0 is estimated through temperature at 28J or 41J CVN impact energy, the predicted fracture toughness values of the three steels are consistent with actual test data. The reference temperature T0 is also estimated through the IGC-parameter correlation and through a combination of empirical formula and multi-temperature method. Both procedures show excellent agreement with test results. The mean value of T0 estimated from T28J, T41J, IGC-parameters and the combination method is denoted by TQ-ave and is then used as the final reference temperature T0 for the Master Curve determination. Accuracy of TQ-ave (and therefore the Master Curve method) is demonstrated by comparison with actual test data of the three RPV steels. It is concluded that Master Curve method provides a reliable procedure for predicting fracture toughness in the transition region utilizing limited CVN impact energy data from open literature.

Statistical assessment of notch toughness against cleavage fracture of ferritic steels

“…Particularly, the impact tests of notched specimens are very popular in the society of materials science and engineering as a cost‐effective approach to determine DBTT and correlate the DBTT and toughness of notched specimens with those of fracture mechanics specimens. For example, Yu, et al summarized the empirical formulas correlating fracture toughness K IC with Charpy impact energy. On one hand, the DBTT approach is expected to be continuously employed in industry, not only because its easiness and low cost but also due to the very rich and valuable experimental data accumulated over the years.…”

Evolution of Impact Properties of 16MND5 Forgings for Nuclear Reactor Pressure Vessel during Thermal Aging at 500°C

“…The effects of thermal aging still call for more attention. Low alloy forging steels are one kind of the most widely used RPV materials, such as French RCC-M 16MND5, German 20MnMoNi55, Japanese SFVV3, as well as ASMESA508-CL3, which just have slight variations in chemical compositions [5]. And the research of these materials are summarized as follow:…”

Effect of non‐uniform reactor cooling on fracture and constraint of a reactor pressure vessel

“…The reactor pressure vessel (RPV) in a nuclear power plant is not replaceable, and thus, its integrity determines the lifetime of the nuclear power plant. During the operation of the plant, the integrity of RPV should be assured, and the brittle failure of the RPV should be excluded . A critical loading for a RPV is pressurized thermal shock (PTS), ie, rapid cooling of sections of the hot and still pressurized RPV by injection of cold emergency coolant, which is the result of the loss‐of‐coolant accidents (LOCAs) .…”

“…Because of the significance and nuclear safety, a lot of work has been done concerning the safety assessment of RPVs under accident scenarios . Both deterministic and probabilistic integrity analyses of an RPV subjected to PTS transient considering uniform RPV cooling have been performed by linear elastic (LEFM) and elastic‐plastic fracture mechanics (EPFM) .…”