Torque operations at Rampion and Humber Gateway offshore wind farms

Wind farm operator, RWE Renewables (RWE) calls on James Fisher Marine Services (JFMS) to support its operations and maintenance programme at two UK wind farms.



Assembled and maintained offshore with critical joints with a life expectancy of in excess of 20 years, offshore wind turbines must be able to face the buffeting of winter seas and gusting storms –and withstand prying forces, vibration and continuous temperature variation in a highly corrosive atmosphere of salt spray, rain and UV. It is because of these factors that asset monitoring and bolt tightening offshore are crucial considerations.

Humber Gateway is a Round 2 windfarm situated off the Yorkshire coast, capable of generating 300 MW of clean energy. While the 400MW Rampion Offshore Wind Farm became the first commissioned off the south coast of England in 2018, following three years of construction.

To ensure it continues to deliver to its full potential throughout its operational life span, James Fisher Marine Services (JFMS) provided a scope of bolt measurement and maintenance working with the customer’s contracted NDT specialist to ensure ongoing integrity of bolted connections which effectively hold the turbine tower upright.




For offshore wind turbine applications, foundation bolting can be the tricky to maintain and difficult to access.

As the industry matures, offshore wind turbine generators (WTGs) are moving further offshore and so the maintenance of these valuable assets and taking precautions to avoid failure is increasing in importance. This is not because of the cost of the bolt or stud; it is the time and expense of maintenance, which is very exacting, and the uncertainty of the system.

A selection of WTGs were singled out for bolt load assessment – seven of 73 at Humber and nine of 116 at Rampion. 



There are a number of bolted flange connections in the WTG, so the safety of these connections are crucial to the structural safety. One of the most critical procedure to maintain the main structural bolts to the correct tension and preload.

RWE manage Humber Gateway and Rampion from local operations and maintenance facilities, in Grimsby and Newhaven respectively, which JFMS supported day-to-day from its renewables base in Lowestoft.

On each of the selected WTGs, JFMS assisted the contracted NDT technician to take precise measurements of all 84 bolts holding the foundation to the lower monopile section, before removing bolts ashore for detailed load testing and analysis.

In the offshore wind industry, every minute of downtime results in a loss of production and revenue. But, where bolting is concerned, significant cost reductions are possible with the right tools and knowledge –as JFMS proved at Humber and Rampion using a range of specialist Hytorc™ Stealth tools to reduce maintenance times while achieving superior results.

However, the biggest challenge for offshore wind farms is accessibility and weather and sea conditions. Regular inspections and maintenance are unavoidable, however.

JFMS has a resource pool of vastly experienced and MJI qualified technicians, strengthened by strategic partner RMI Engineering Ltd., that have provided operations and maintenance support across a number of wind farms, including those in the region of the Thames Estuary.

An unusually heavy job for the bolting technicians, this work scope included the transfer of ultrasonic thickness (UT) measurement and bolt tensioning equipment to the turbine foundation, the removal of bolts for “load to zero” measurements, the installation of new bolts –positioned and tightened to precise levels of torque and tension, and transferring all equipment back to the operations vessel. 

Work across the wind farms took place over a period of 36 days, where rope technicians worked in confined spaces, overcoming extreme conditions to do so, down in the bowels of the WTG.

Confined space working is a high-risk operation that requires robust planning, thorough risk assessment, high specification equipment, trained, skilled and well-drilled teams as well as project specific procedures and method statements.

Throughout any operation of this nature, it is vital for all team members to ensure constant communications between those within, and outside of, the confined space area as well as between the confined space team and those involved in rescue operations, in this case the CTV crew. Monitoring environmental conditions frequently is key to ensuring there is no increased or additional risk to anyone involved.