The exhaust systems of gas turbines are subject to both rotational loosening due to operational loads and non-rotational loosening caused by thermal cycling.
In this particular case, the double/ jam nut method, combined with tab washers, was initially used to secure the exhaust system flanges of a gas turbine. However, this method frequently resulted in loosening due to improper bolt tension (preload) application. Achieving the correct preload is critical for flanges: excessive preload can cause gasket creep, while insufficient preload leaves them vulnerable to rotational loosening due to operational loads.
Uniform load distribution across the flanges is also essential. Consistent preload ensures that each bolt evenly clamps the flanges, maintaining equal pressure across the gasket or contact surface. This uniformity is vital to prevent leaks and maintain the integrity of the seal.
The introduction of HARDLOCK® nuts effectively resolved the loosening issues associated with the jam nut method. The HARDLOCK® nut’s wedge-incorporated design creates a locking effect independent of preload. This allows for the safe application of lower preload, minimizing the risk of gasket creep while still preventing rotational loosening.
Additionally, the HARDLOCK® nut design ensures that tightening the top nut does not increase the preload on the bottom nut, simplifying the process of achieving uniform load distribution.
As a result, safety was significantly improved by eliminating the risk of flange loosening and reducing the likelihood of gas leaks.