The invention relates to a device and a method for performing maintenance on an apparatus. The device has a flow duct with a wall section in which at least one apparatus which projects into the flow duct and which is to be reworked after a certain operating time is arranged. A vessel which is open towards the wall section is arranged to as to be movable relative to the wall section in such a way that in an open position it is arranged at a distance from the apparatus, and in a second position forms, together with the wall section, a sealed volume which is separated from the rest of the flow duct and in which the maintenance of the apparatus is performed.