The present invention relates to a pipe unit (3) in a pipeline (1) for a gaseous medium. The pipe unit (3) comprises a tubular body (11) with two end portions and a contact surface (11b1, 11c1) which is close to at least one of said end portions and is adapted to being placed in contact with a contact surface (2a1, 4a1) of an adjoining pipe (2, 4) in the pipeline (1). Said contact surfaces (2a1, 4a1, 1 lb1 11c1) are so configured that the pipe unit (3) in a connected state has mobility relative to the adjoining pipe (2, 4). The pipe unit (3) comprises a tubular flexible sealing means (8, 10) which at a first end (8a, 10a) is firmly attached to the tubular body (1 ) and at a second end has a flange element (8b, 10b) which is detachably connectable to a flange element (2b, 4b) of the adjoining pipe (2, 4) by a connecting means (7, 9).