In bolted flange joints of flexible constructional elements, bolts are subjected not only to tension and torsion but also to bending loads. Identification of straining of each bolt is only possible by means of numerical methods e.g. the finite element method. In the case of large objects, the calculation problem is faithful projection of the phenomena occurring in direct zone of the contact of screw-nut pair. The application of global equivalent models of the whole joint is necessary in order to make it possible to precisely determine internal loads in individual bolts and then local models to establish stress fields necessary to assign durability. Calculation methodology based on the construction of two coherent models has been described: global - for the entire flange joint, and local - for a single bolt joint. The elaborated methodology was applied to evaluate a flange joint in a heat exchanger with rotating heating surfaces that was subject to damage. The causes of damage of the flange joint were determined.