Influence of pre-exposure on low-temperature embrittlement of alloy 82 welds in simulated PWR primary water environment

Abstract

This study focused on the low-temperature embrittlement of alloy 82 welds in a simulated PWR primary water environment, and in particular on assessing the influence of pre-exposure on the embrittlement in this environment. In most cases, the hydrogen amount inserted during pre-exposure in the simulated PWR primary water without mechanical loading is low due to the barrier effect of the oxide layer, so it does not significantly influence the tensile behaviour of the welds. On the contrary, hydrogen absorption in the outer layer of the tensile specimens is promoted by the breakdown of the oxide layer when the tensile tests are carried out in the simulated PWR primary water environment. This weakens the outer layer, leading to crack initiation; then, crack propagation is controlled by the hydrogen amount at the crack tip. Hydrogen transport by mobile dislocations and hydrogen diffusion promoted by the dislocation network help to establish the critical amount of hydrogen at the crack tip. In addition, crack propagation is also probably enhanced by the effect of hydrogen on the corrosion behaviour of the weld, i.e., destabilisation of the passive film and increased dissolution processes.