pipes 9 10 welded into terminal piece 2 tubular support members 11 12 are welded between pipes 9 10 and terminal piece 2 and form an outer cover along the axial extent of inner protective tubes 7 8 so that annular spaces are defined between inner protective tubes and support members 11 12 an annular support pad 13 14 is placed in each annular space the support pads 13 14 are held in place axially on the inner protective tubes 7 8 by radially protruding corrugations 15 16 therein which corrugations extend into the pads 13 14 the support members 11 12 radially contain the support pads 13 14 and also form circular axial contact surfaces 17 18 which support the pads 13 14 in both axial directions in this manner support pads 13 14 are secured within the annular spaces defined by the inner protective tubes 7 8 and the support member 11 12 moreover at the same time inner protective tubes 7 8 are connected to the support members 11 12 and as a result terminal pieces 1 2 are interconnected flexibly and via support pads 13 14 in an elastically damped manner the connection members formed respectively by parts 7 11 13 and parts 8 12 14 for terminal pieces 1 2 assure that terminal pieces 1 2 are held in a position corresponding to the middle of guide elements 3 as is evident from the drawings the interior of guide element 3 is sealed by support pads 13 14 against the gas which streams through flow paths 5 6 further flow paths 5 and 6 are sealed off from each other so that exchange or commingling of their respective flowing media is prevented the structure depicted in fig1 and.