The present invention relates to pipe fittings essentially used in extreme conditions such as high and low pressures, high vacuum, high and low temperatures, aggressive media and the like. This invention can be used in motor vehicle construction, in aviation, in astronautics, in nuclear technology, in the ship-building industry as well as in other industrial branches. The sealing is achieved using an elastic insert which is centered by placing the same inside or outside a centering insert so that they are brought into contact upon mutual axial displacement in order to maintain the alignment and to prevent any displacement of the centering insert in the transverse plane. During the pipe constriction process, the method involves equalising the contact pressures on the toroidal protrusions of the elastic insert. In a second embodiment, each end face of the centering insert is provided with at least two flat and slit adjustment rings, and the constriction of the pipes occurs before bringing into tight contact the end faces of the pipes to be connected, the adjustment rings and the end faces of the centering insert. The seal includes a centering insert coaxially mounted relative to the elastic insert so that they can be brought into contact upon mutual axial displacement.