The Effect of a Low Constraint Geometry on Measured T0 Values for a Nuclear Reactor Pressure Vessel Ferritic Steel

Current requirements for assessing the fracture toughness of reactor pressure vessel (RPV) ferritic steels are potentially overly conservative due to the employment of high constraint geometries such as compact tension (C(T)) or single edge notch bend, SEN(B), specimens for material testing. These high constraint conditions are not representative of the actual conditions experienced by the RPV in service. If this conservatism could be reduced, more appropriate predictions for RPV lifetime extension could become a possibility. In this study, a known low constraint geometry, single edge notch tension, SEN(T), has been tested alongside the higher constraint SEN(B) specimen in order to compare measured T0 and fracture toughness values for both cases. Finite element analyses have also been conducted for both geometries in order to measure T-stress and calculate Q values thereby allowing quantification of the level of constraint for both geometries. Eight SEN(B) and eight SEN(T) specimens were tested with dimensions 24 × 254 × 96 mm and 20 × 20 × 200 mm, respectively. Testing was conducted at sub-zero temperatures, as close to the T0 as possible, in accordance with the guidelines presented in ASTM E1921-17a. Contrary to expected behaviour the SEN(T) specimen indicated a higher (less negative) T0 then the SEN(B) specimen. The reason for these results are explored in this paper.