Methods of Increasing the Efficiency of Tightening Monitoring of Threaded Connections (Survey of Published Studies)
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INFORMATION METHODS OF INCREASING THE EFFICIENCY OF TIGHTENING MONITORING OF THREADED CONNECTIONS (SURVEY OF PUBLISHED STUDIES) M. M. Matlin, V. A. Kazankin, and E. N. Kazankina
UDC 620.81
A survey of methods of monitoring the tightness of threaded connections that can be used in the assembly, operation, and repair of equipment in the chemical and oil and gas branches of industry is presented. Keywords: threaded connections, controlled tightening, ultimate strength, yield limit.
Threaded connections are used for 70% of the parts of modern industrial equipment. It is especially important to ensure the reliability of threaded connections (when assembled and in the course of maintenance) in the operation and repair of equipment in the chemical and oil-and-gas branches of industry in connection with processing and transportation of corrosive and highly inflammable liquids under high pressures and temperatures. Only controlled tightening is used to assemble critical threaded connections with control of the angle of rotation of the nut, the length of the bolt, or (most often) relative to the torque relative to a special key (dynamometric key or limit moment). The objective of the present article is to increase the precision of determining the tightening force of threaded connections. The admissible magnitudes of the tightening torque of bolts [1] depend on the diameter of the bolt and on the strength of the material of the bolt. The following formulas for use in approximate determination of the required bolt screw-in torque Tscrew that assures attainment of the required tightening force Ftight of a bolt are presented in [2]:
Tscrew = fFtight d ,
(1)
Tscrew = 0.07σ 0.2 d 3 ,
(2)
where f is the friction coefficient; Ftight – bolt tightening force; d – diameter of bolt; and σ 0.2 – yield limit of the material of the bolt. It should be emphasized that there two difficulties that hinder achieving reliable assurance of a required tightening force. The first difficulty arises from the fact that only ∼ 15% of the key torque strength is consumed in the creation of the tensile force in the bolt in the course of tightening of a threaded connection, while 85% is consumed in friction in the screw thread and the face of the nut. Thus, the readings of a dynamometric key are basically
Volgograd State Technical University, Russia; e-mail: [email protected]. Translated from Khimicheskoe i Neftegazovoe Mashinostroenie, Vol. 56, No. 7, pp. 40−42, July, 2020. 582
0009-2355/20/0708-0582
© 2020
Springer Science+Business Media, LLC
METHODS OF INCREASING THE EFFICIENCY OF TIGHTENING MONITORING OF THREADED CONNECTIONS
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Fig. 1. Schematic diagram of nut (Inventor’s Certificate No. 311057): 1 – thread bushing, 2 – dowels, 3 – female sleeve with key hexahedron.
determined by the friction coefficient the magnitude of which depends on the roughness of the thread surface, the pressure in the contact, the errors in the step and angle of the thread profile, the material of the thread parts, the type of coating, lubrication conditions, recur
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