Prediction of long term crevice corrosion and hydrogen embrittlement behavior of ASTM grade-12 titanium

Crevice corrosion and hydrogen embrittlement are potential failure modes of Grade-12 titanium high-level nuclear waste containers emplaced in rock salt repositories. A method is presented to estimate the environment domains for which immunity to these failure modes will exist for periods of hundreds of years. The estimation is based on the identification and quantification of mechanisms involved. Macroscopic concentration cell formation is responsible for crevice corrosion. The cell formation is accompanied by oxygen depletion, potential drop, anion accumulation and acidification inside the crevice. This process is quantified by simple mass balance equations which show that the immunity domain is a function of the time the container is exposed to the corrosion environment. Strain induced hydride formation is responsible for hydrogen assisted crack initiation. A simple model for slow crack growth is developed using data on growth rates measured at various temperatures. The parameters obtained in the model are used to estimate the threshold stress intensity and hydrogen solubility limit in the alloy at infinite container service time. This value gives a crack size below which container failure will not occur for a given applied stress and hydrogen concentration, and a hydrogen concentration limit at a given stress intensity. 37 references, 5 figures, 4 tables