Methods of Monitoring of the Threaded Connections (A Review)

Threaded connections, including connected parts and threaded fasteners (bolts, screws, studs, nuts, washers), are widely used in industry, construction, and everyday life due to the numerous advantages they have over other types of connections. However, under conditions of variable loads, a weakening of tightening of threaded connections is observed up to the opening of their joint and destruction of fasteners. A sign of a loosening of the tightening of threaded connections is a decrease in the axial force (stress) in the rod of a bolt (stud, screw), and a sign of incipient destruction of the connection is a crack in the fasteners. Continuous monitoring of the measured parameters and comparison of their values with threshold values is carried out by monitoring, respectively, the magnitudes of stresses and cracks in bolts (studs, screws). This article discusses the basic principles, gives comparative characteristics, analyzes the advantages and disadvantages of the most well-known methods for monitoring threaded connections with large fasteners (d = 30 ...200 mm), and also discusses the possibility of using some of them for monitoring threaded connections of turbine equipment of power plants.