A device for the fluid-tight sealing and separation of a pipe section by means of an ultrasonic welding device, including a sonotrode with a first welding surface, an anvil with a second welding surface that is assigned to the first welding surface, and a separating element which starts from the sonotrode and extends past the first welding surface. In order to be able to separate a section of a pipe in such a way that the pipe is sealed in a fluid-tight manner regardless of the side on which the section is located and without having to change tools or reposition the ultrasonic welding device, the sonotrode is provided with two first welding surfaces which are placed at a distance from each other and to which two second welding surfaces of the anvil are assigned, the separating element is disposed between the two first welding surfaces, and a recess which is located between the two second welding surfaces of the anvil is assigned to the separating element.