A pipe unit for arrangement in a conduit for a gaseous medium, comprising a pipe-shaped body, a pipe-shaped flexible sealing element, which is fixedly attached at a first end outside the pipe-shaped body and which comprises a flange element at a second end. The flange element is detachably attachable to a flange element in a connecting pipe in the conduit, in order to, when the flange elements are fixed to each other and the pipe unit is accordingly connected with the connecting pipe, to allow movement between the pipe-shaped body and the connecting pipe via the sealing element's flexibility. A mutual fixation of said flange element forms the only touching connection of the pipe unit to said connecting pipe.