Comparative study on loosening of anti-loosening bolt and standard bolt system

Abstract

In general, bolted connections are exposed to vibrations or repeated over-loads that could lead to self-loosening due to loss of preload. Pre-tensioned bolts in ring flanges are critical parts in Offshore Floating Wind Power Systems, and normally a certain percentage of the installed bolt connections are checked and re-tightened every year. This re-tightening is often done at a high cost and a short weather window due to strong winds and high waves. In this paper, three bolt dimensions (M20, M30 and M42) of the anti-loosening bolt system have been tested. The M30 and M42 bolt systems were preloaded and exposed to transverse oscillating loading, and the loss of preload as a function of load amplitude and number of cycles were measured and compared to standard bolts of HV type, exposed identically. The tested novel bolt system has shown superior capacities to withstand self-loosening, compared to standard bolts.