Simulation of phase transitions in the IMC-hydrogen systems in the frames of perturbation theory provides accurate description of main characteristics of the phase diagrams in the wide range of hydrogen pressures. The data obtained for thermodynamic parameters of the alpha ->beta transitions gives a possibility to describe hydrogen solubility in TiMn1.5 at the pressures up to 600 atm; the parameters of the critical point of the alpha ->beta equilibriums are also obtained. The proposed calculation scheme uses no fitting parameters or empirical correlations and leans upon atomic characteristics of the hydrogen subsystem and metallic matrix which are physically meaningful. (C) 2010 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.