Improving reliability of drill pipe by strengthening of thread connections of its elements

Abstract

It is recommended to include surface strengthening by plastic deformation into technological process of manufacturing boring pipes and nipples connecting 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 vibrationalcentrifugal 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 vibrationalcentrifugal 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 vibrationalcentrifugal 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 vibrationalcentrifugal 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 cen trifugal 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 con nections of their elements. Industrial implementation of vibrationalcentrifugal 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.

Development of the finishing and strengthening technological operations using SADT-technologies

“…The quality parameters of the mechanical engineering parts are characterized by the dimensional accuracy, quality parameters of surface layer, operational characteristics and reliability indicators. Providing of the production quality is the most important problem of modern mechanical engineering [4]- [6].…”

“…The machine properties, that provide its service function and determine the operational properties, are formed during the technological processes of production parts by means of interaction of different technological objects [4], [17].…”

“…The method of vibrational-centrifugal surface strengthening (VCSS), developed at the Lviv Polytechnic National University, refers to dynamic methods of surface plastic deformation. It is applied at the finishing and hardening operations of technological processes of part processing for providing of required technical and operational characteristics [4].…”

“…The factors, which influence on the change of the geometrical and physical-mechanical parameters of the surface quality of the part are the feed rate VS (X1), adduced rigidity of the sections of elastic systems cad. (X2), the number of device passes n (X3), the weight of the reinforcers of the device mr (X4), the current in the coils of the drive solenoids I (X5) [4]. The influence of technological parameters of vibration-centrifugal hardening on geometric (mean arithmetic deviation of the Ra profile, mean step of profile irregularities Smw, etc.)…”

“…The limit values of technological factors are taken as following: VS = 35-135 mm/min, cad. = 3.317/7.471⋅10 5 N/m, n = 1-3, mr = 1.8-3.0 kg, I = 0.75-1.25 A [4].…”