Abstract: The method of manufacturing polymetallic pipes according to the invention consists of preparing the contacting surfaces of pipe billets, sealing off the gap between the billets at their ends and forming a multilayer pipe billet, heating said billet, placing it into a die and sealing off the space of the pipe billet, and filling said space with a fluid medium for exerting pressure on the internal surface of the billet, said pressure being sufficient for producing a diffusion joint.According to the invention, the temperature gradient in the body of the pipe billet is distributed so that the temperature at one end of the billet is lower than it is in its other parts.

Abstract: A device for use in piercing and plugging mills, comprising a rod with a plug and a gear, for keeping the rod from longitudinal displacements under the effect of the load arising during the piercing or plugging. The gear includes a fixed thrust bearing accommodating a revolving casing through which passes the rod that reciprocates in operation. A part of the internal surface of the revolving casing forms a working cone that faces the plug with its base. The gear also includes a lock to fix the rod when piercing or plugging a billet, and preferably mounted on the rod, and a drive for carrying the rod with the plug. The lock mounts a spring-biased cone positively encompassed round the circumference with radially floating cams. Before piercing, the spring-biased cone is slightly drawn off by the spring from the cams so that the latter can enter the lock which is then able to enter the casing.