Critical pitting and crevice temperatures have been measured for many alloys using open-circuit potential tests in standard electrolytes, such as the 10 % FeCl₃ or mixtures of NaCl with FeCl₃ and CuCl₂ for many years. Although these measurements are primarily used for alloy ranking purposes, there is interest in using them for applications with different solution chemistries. On the other hand, critical pitting temperature has been modeled in terms of the threshold condition for the formation of metal-chloride salt film or the maintenance of a critical metal-chloride concentration in the pit environment, using artificial pit electrodes and relatively simple solutions, such as NaCl. This paper addresses a modeling approach to bridge the gap between the immersion tests, electrochemical measurements, and theory. An irreversible thermodynamics model is combined with concentrated electrolyte speciation model to predict the critical crevice temperature of several Ni-Fe-Cr-Mo-W alloys. The model computes the repassivation and corrosion potentials of alloys as functions of solution composition and temperature. The superposition of these parameters provide a conservative estimate of the critical crevice corrosion temperature. The predicted values are validated against critical crevice temperature data reported in the literature. The effect of aqueous electrolyte composition on critical crevice temperature is calculated and compared to field experience. The model is further extended to mixed solvent systems, where the solvent is a non-aqueous environment. The implications of the model are discussed.