Abstract
In this study, the threshold stress intensity factors for the hydrogen assisted crack initiation, KIH were compared using the high and low toughness welded joints simulated under two different PWHT conditions within the 2.25Cr-1Mo-V steel reactor fabricating specifications by reproducing the hydrogen embrittlement factors predicted under each operating conditions such as startup, steady-state operation and shutdown into 1T-C(T) specimens, rising and holding load tests. First of all, in the reproduce of startup conditions, the rising load tests were performed under 20 MPa hydrogen pressure at room temperature. As the results, quasi-cleavage crack initiation mode was observed during slow rising load in both high and low toughness welded joints. However, in the low toughness welded joint, fast fracture before the onset of 5 % nonlinearity occurred, and the fracture toughness due to hydrogen embrittlement, KIC-H was recognized. Secondary, in the reproduce of steady-state operating conditions, the threshold for hydrogen assisted crack initiation was determined in the same way as reproduce of startup conditions, and the holding load tests were conducted where the hydrogen environment and load for the threshold for hydrogen assisted crack initiation were maintained for up to 10 days. As the results, it was observed that quasi-cleavage crack growth continued during the load holding period in both high and low toughness welded joints. The crack growth rate in the high and low toughness welded joints were modeled respectively, by numerically introducing the relationship between da/dt and K based on the correlation between the quasi-cleavage crack growth and the load line displacement. Finally, in the reproduce of shutdown conditions, the rising load tests were performed in air at 150 °C using the 1T-C(T) specimen that had been pre-charged with hydrogen. As the results, there was almost no difference in the values of KIH between high and low toughness welded joints.
