For maintenance staff the energy sector is a demanding environment, frequently requiring working at height and in all sorts of weathers. On land access is generally straightforward, except in the more remote areas, but offshore in the marine environment access is much more hazardous.
Increasing renewables developments are taking place offshore with the massive capacity of offshore wind starting to be tapped, primarily in Europe, with over 8GW of installed capacity, and in the United States. [Engerati-Europe’s Offshore Wind Market Levels Off] As the numbers of turbines increase, so too will the maintenance requirements.
Some of the challenges of offshore wind turbine access include the swell, which can be unpredictable with up-down movements of several metres, the human element of interaction between the person transferring and a boat deckhand, and then the ladder climb up the turbine.
Thus, key design considerations pertain to the boat landing/ladder design, the access/egress methodology, and the design of the transfer vessel.
Access to offshore wind turbines
The UK Carbon Trust’s Offshore Wind Accelerator currently has a research study under way to compare the performance of access solutions. Current selection methods for vessels or transfer systems for specific sites are highly subjective and comparative measured data of their performance is largely not available. The result of this lack of information is uncertainty of wind farm accessibility in project business cases and potentially sub-optimal combination of vessels, fenders and transfer systems for a site.
Through a performance metrics validation project the aim is to develop the access performance of four initial baseline vessels that are representative of the current vessels used today in the offshore wind industry. The performance is being determined through a combination of numerical modelling, tank testing and full-scale sea trials to provide baseline performance plots defining how vessels perform in different sea states. This in turn will provide input for better operations and maintenance modelling and fleet definition.
Standardized boat landing
Another project being undertaken by the IMCA, the offshore, marine and underwater engineering trade association, is focused on developing a standardized boat landing arrangement on offshore wind turbines in European waters. This was perceived as desirable to improve safety and minimize costs of modifying boat fenders.
From a database that was compiled from a questionnaire submitted to stakeholders across Europe, it is apparent that de facto standards exist for several key parameters related to boat landing designs and the development of a broadly acceptable standardized arrangement is anticipated.
The work has also identified a number of areas where further research is required, the most important of which is the boat impact loading. Out of the 24 projects where data were collected, only two were able to provide this figure, indicating a lack of knowledge of the limits of boat landing systems and design inconsistencies.
An initiative by Siemens, one of the major offshore wind turbine developers, has focused on improving the transfer method with a 'one-hand operated quick release' transfer connector. The aim of this ‘FROG’ connector is to reduce the involvement of the boat deckhand while also requiring minimal time of connection to the self-retracting lifeline prior to access and instant release in the moment of egress, as well as the option to perform a 'cut away' in the event of equipment failure.
A novel ladder design
Fishermen’s Energy and Keystone Engineering, which plan to install wind turbines off the coast of Atlantic City, New Jersey as part of the US Department of Energy’s advanced offshore wind demonstration, has been taking a look at ladder design.
Generally ladder access requires the worker to step from the vessel forward across a gap to the ladder. In the US regulations call for a narrower gap between the boat and the ladder which can be more dangerous for the worker because of the unpredictable motion of the boat. The approach taken by the two companies is to rotate the ladder by 90 degrees so that the vessel deck can be placed as close as possible to the ladder rail and allow the worker to safely side step onto the ladder. In the event of an accidental fall, the worker wouldn’t be pinned between the vessel and the ladder but, instead would fall in a clear space protected by the fender system.