The paper presents recently published literature research on the tightness and strength of flange joints. These could influence both the calculation and the maintenance of flange joints. Some of the research results have been compared to normative stipulations currently used in the calculation of flange joints. The presentation covers: – the influence of sealing gasket design and screw load on sealing; – the influence of creep on screw relaxation, and thereby on gasket sealing; – cracking in flange joints; – the influence of an additional axial force of flange joints on the rotation and on the deformation of flange joint components; – flanges without sealing gasket; – the influence of the method of flange joint bolt tightening on the uniformity of bolts loading and tightness.

"Starting from the concept of deterioration, using the principle of critical energy and considering the nonlinear, power law, behavior of the sample, or of the mechanical structure, there were proposed relations for critical stresses in the case of: – uniaxial static loading with normal stress or with shear stress, or simultaneously with normal and shear stress; – uniaxial cyclic loading with one block of normal stress or one block of shear stress, as well as simultaneous with a block of normal stress and one block of shear stress, taking into account the deterioration due to crack. Failure criteria for cracked mechanical structures, uniaxial statically or cyclically loaded, have been developed. The critical stresses calculated for cracked samples compared with experimental results reported in literature, have shown good agreement between them. "