Evaluation of fracture toughness characteristics for nuclear piping using various types of specimens

The leak-before-break (LBB) concept is based on the fracture resistance curve obtained by J-R tests for various types of specimens. But fracture toughness data of various types of specimens are different. For example, the estimates for fracture toughness of standard specimens are conservative when compared to the fracture toughness of real pipes because of the difference of the constraint effect between real pipes and standard specimens. Therefore, to estimate the integrity of real pipes based on elastic–plastic fracture mechanics, we have to first establish the relations among real pipes, standard CT specimens and curved CT specimens. In this study, we perform fracture toughness tests of nuclear piping materials using various types of specimens. And each J-R curve considered in the constraint effect is compared. The experimental results showed that a curved CT specimen is similar to the cases of pipes with small crack angles (60° and 120°) and a CT specimen is similar to the case of pipes with the crack length of 180°. Also, the Q-stress for curved CT specimens is higher than that of pure bending pipe specimens and lower than that of CT specimens.