Selecting the Method for Pre-tightening Threaded Connections of Heavy Engineering Objects

Abstract

The choice and application pre-tightening method of the threaded connection for each specific technical object is determined both by the specifics of production and by established traditions that have passed many years of experience in operational tests. At the same time, there is no formalized scientific justification for the decision on the choice of the tightening method for the threaded connection. In this work, based on the results of a review of the known methods of pre-tightening of threaded connections, the choice of tightening the impeller with the shaft of axial hydraulic turbines is justified. An assessment of the probability of failure-free operation of threaded connections is proposed, taking into account the applied tightening method and its weakening during operation. As a result of the research, it was found that for the known methods of implementing and controlling the tightening of threaded connections, namely with a torque wrench, according to the rotation angle, according to the deformation of the elastic washer, according to the elongation of the bolt, 20% weakening corresponds to the probability of failure-free operation equal to 0.5. The method of tightening with a torque wrench has the softest effect on the probability of failure-free operation according to the criterion of relaxation of tightening forces. The elongation measurement tightening method up to 15% loosening guarantees high reliable operation of the threaded connection with a failure rate of 0.99. The results obtained will make it possible to scientifically select a method for the implementation and control of tightening of threaded connections of heavy engineering objects, depending on their purpose and design features.