The safety of offshore assets such as wind turbines, offshore cranes, and turret mooring systems partly relies on the integrity of heavy-duty bolted joints. These critical connections can be of different dimensions and exposed to monotonic and cyclic loading. Despite being small components of a structure, bolts need to be maintained appropriately to ensure structural safety and reliability. The integrity of bolted joints can be assured by checking for adequate preload. In addition, fatigue failure resulting from preload loss is of primary concern, as it can occur suddenly without any visible changes. Hence, bolts should be re-tightened periodically to ensure sufficient preload. However, in offshore conditions, this countermeasure leads to high maintenance costs while exposing the crew to unfavourable conditions and risks.

This research focuses on the feasibility of condition-based maintenance of bolts using ultrasonic waves. An energy attenuation method has been implemented for this feasibility research. The main objective is to establish a proper methodology and hypotheses for preload detection. Furthermore, along with preload detection, the feasibility of crack detection was investigated. Finally, the proposed methodology and hypotheses were validated by performing experiments and numerical simulations.

The experimental and numerical results verify the proposed methodology by showing an increasing trend in the energy and the power of the transmitted ultrasonic wave for increasing preload. Also, the feasibility of crack detection using the same setup has been positively evaluated.

The obtained results suggest that the ultrasonic waves can be employed to monitor bolts for condition-based maintenance. Additionally, a number of relevant research activities are recommended based on this study.