It is recommended to include surface strengthening by plastic deformation into them, which are made of 40ХН steel. The main task of this strengthening operation is redistribution of technological tensile stresses in the material of thread roots, surface strengthening of the metal in the thread roots and formation of compression stresses in the metal, which are able to resist working stresses. The analysis of existing methods of surface plastic deformation showed that the only suitable method for qualitative treatment of thread roots is the method of vibrational-centrifugal strengthening. This method belongs to the group of dynamic methods of surface plastic deformation (SPD) and provision of high level of energy of metal deformation of strengthened part metal is its peculiar feature and advantage. Purpose. Development of the method of vibrational-centrifugal strengthening suitable for qualitative strengthening of thread surfaces, its adaptation to strengthening the outer taper thread, definition of the key technological parameters of strengthening treatment. The main tasks of the research were development and production of strengthening appliances suitable for strengthening the taper thread, functioning on the fundamental principles of vibrational-centrifugal treatment. Development of schematics of original, out of standard vibration machines for strengthening the outer taper thread of boring pipes and nipples connecting them. Methodology. Based on the theory of statistical similarity of fatigue failure, methods are proposed for defining mass reduction and materials consumption of cylinders as a result of efficient strengthening of their inner and outer cylindrical surfaces by means of vibrational-centrifugal treatment. Findings. As a basis of the structure of the developed appliances for strengthening thread roots of taper thread, there is taken provision of dynamic impact interaction of deformable rollers; whose shape is similar to the thread root profile, through rolling of a massive roller. Due to a small area of contact of a deformable roller with thread root material and large values of deforming centrifugal force developed by the moving roller, the thread root metal is peened reliably and, most importantly, compression stress develops in it. Originality. For the first time, highly efficient equipment for dynamic strengthening of thread surfaces has been developed which knows no equals in strengthening treatment internationally. Practical value. The practical value is in improving reliability of drill pipes due to enhancing material strength of thread connections of their elements. Industrial implementation of vibrational-centrifugal strengthening treatment of thread elements of drill pipes, according to the authors, will decrease the number of cases of destruction of pipe constituents, which will contribute to decreasing repair and servicing time for drilling equipment, and will increase the borehole drilling rate.

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