The invention relates to a device for welding the end faces of thin-walled jackets (12) on a welding plane, said device comprising two cylindrical positioning receiving units (1), which center the jackets (12) to be welded in relation to their outer diameters, both receiving units (1) being located on an alignment base flush with one another and being axially displaceable. A deformable, annular, membrane-type heat exchanger is situated on the exterior of each receiving unit (1), said heat exchanger being formed from a set of sheets (2) consisting of heat-resistant material that are separated from one another. The lower end of the sheets is designed to be in thermal contact with the jacket (12).