A computational procedure for construction of approximate phase bounda
ries without iterative determination of equilibrium phase compositions
has been developed. The method, which is very easy to implement, redu
ces the equilibrium conditions for mixtures containing an arbitrary nu
mber of components to only two equations to be solved for temperature
and pressure. In addition a refinement procedure is described for exac
t calculation of points on the phase boundary, which enables fast conv
ergence in the critical region without the requirement for composition
derivatives of the component fugacity coefficients.