The invention concerns an integral threaded or sleeved assembly of two metal tubes provided or not with an internal coating and in particular designed to contain internally a corrosive fluid. The assembly male element(s) (1) each comprise in the direction of their open end a threaded part (13) and an unthreaded part, the latter comprising successively a sealing metal surface (14), a ring-shaped transverse support surface (15) and a nozzle surface (16) which joins the tube internal peripheral surface (10) via a radial surface (17) called inner end. The female element(s) comprise elements corresponding to the male elements and co-operating therewith. A sealing ring (40) is set between the inner end ring-shaped surfaces (17), (17') and prevents the liquid phase from seeping into the assembly. The assembly is characterised in that it comprises sealing metal male surfaces (14) arranged between threaded part (13) and support surface (15) and by the presence of a clearance between the nozzle outer peripheral surface (16) and the reinforcement inner peripheral surface (26) opposite the female element (2). The invention includes in particular special solutions when the tubes (10') are provided with an internal coating particularly in the form of tubes with inner lining (51), (51'). In such a case, flanges (60), (60') are provided to provide continuity for the coating on the ring-shaped end surfaces.