Offshore Wind Innovation: Boltight® Hydraulic Tensioning in Action

Renewable energy offers a sustainable path forward, replacing finite fossil fuels with naturally replenished resources like solar, wind, and hydropower. It is a vital necessity because while it supplies homes and businesses with power and electricity, it also provides health and environmental benefits by reducing air pollution and combating climate change.

One such initiative is the Jeonnam Offshore Wind Power Project, a 96-megawatt (MW) offshore wind farm located in the Yellow Sea, Jeollanam-do, South Korea. It consists of ten turbines, each with a capacity of 9.6 MW. The project is expected to supply electricity to approximately 90,000 households and commenced commercial operation in May 2025.

Looking ahead, additional offshore wind farms with a capacity of 399 MW each are planned for Phase 2 and Phase 3. Once the entire development is completed, the Jeonnam Offshore Wind Power Project will generate a total of around 900 MW, positioning it as the largest offshore wind cluster in Korea.

BACKGROUND

The project involved two Korean companies: one designs and manufactures plants and equipment for various industrial sectors and the other manufactures and installs steel structures, high-strength concrete piles, and precast concrete. Together they manufacture the monopile foundation (MP) and transition piece (TP) to create the MP-TP flange joint.

This bolted ring flange design is a safer alternative to outdated grouted connections which were prone to failure and turbine slippage. It utilizes several large-diameter bolts to ensure a secure and stable connection to support the turbine’s tower. These high-tension joints are pivotal in maintaining structural integrity under severe offshore conditions, ensuring the long-term stability and sustainable operation of the wind farm.

THE CHALLENGE

The installation of high-tension joints in offshore wind farms demands precision tensioning equipment where operators must execute the process safely and accurately. This becomes even more complex when considering the confined space inside wind turbine towers and the need to fasten 124 bolts with M72 multi-stage tensioners.

Operators must manage heavy equipment, ensure accurate load measurements, and maintain safety standards, all while working in challenging environmental conditions.

THE SOLUTION

Specifically designed to meet the technical and environmental demands of the wind energy industry, Boltight® engineers delivered a cutting-edge hydraulic tensioning system to maximize precision, reliability, and efficiency in tensioning operations. The system includes Typhoon+ multi-stage tensioners, pump and hose assembly, an Echometer ultrasonic bolt measurement tool for verifying the clamp force, and a carriage system enabling operators to handle heavy-duty tensioners for large bolts with ease.

Boltight Typhoon+ multi-stage tensioners have been developed to meet the technical and environmental demands of the wind energy market.

Key product benefits:

• Fast, automatic spring return design removes the need for any manual input
• Improved seal technology enhances performance under high cycle usage
• Internal fail-safe technology keeps the tensioner securely on the bolt
• High-grade material puller bar maximizes cycle life, allowing for long service intervals
• Improved spring-loaded auto engagement gear-driven nut rotating socket with a geared drive requires low maintenance
• Unique surface finish provides long-lasting protection in harsh and difficult working environments

The Echometer is a portable tool that uses ultrasonics to measure the elongation, stress, and load in fasteners. It offers quick and accurate measurements.

Key product benefits:

• Easy to operate
• Compact and durable
• Minimal operator training required
• Provides elongation, load, stress, and strain measurements
• Accurate and reliable
• Simple data recording and reporting

The Boltight carriage system has been specifically designed to lift and move heavy equipment inside the restricted working environment of a wind turbine tower. Operators work in a confined space to fasten 124 bolts with an M72 multi-stage tensioner.

Key product benefits:

• Four air cylinders neutralize the weight, allowing for effortless handling of a 60 kg multi-stage tensioner
• Enables safe and convenient operation inside narrow environments such as wind turbine towers without the need for hoists
• Pre-set wall distance ensures the carriage naturally aligns in place, making bolt-to-bolt transitions quicker and more accurate
• Fall-prevention guides, built-in safety stops, and ergonomic handles minimize risks and protect the operator during operation
• Flexible and easy to maintain

To ensure successful implementation of its tensioning solutions, Nord-Lock Group provided a comprehensive five-hour training session led by Boltight engineers, combining theoretical instruction with hands-on practice. Operators gained a solid understanding of preload principles and the mechanics of bolt tensioning before moving on to the practical installation and pressurization of the hydraulic tensioners. They learned to identify and troubleshoot potential issues during operation and were trained to use the Echometer tools to verify accurate bolt load measurements. This immersive training empowered the team to perform tensioning tasks with confidence, precision, and safety in the demanding environment of offshore wind turbine installation.

CONCLUSION

With the expertise and support of the Nord-Lock Group and Boltight, the offshore wind farm project successfully commenced commercial operation in May 2025.By integrating state-of-the-art Boltight tensioning solutions into the MP-TP flange joint, this project ensures both safety and long-term reliability under challenging offshore conditions. Combined with specialized tools like the Typhoon+ multi-stage tensioners, Echometer, and custom carriage system, and backed by expert training, Boltight empowers operators to achieve accuracy, efficiency, and confidence in every step of the installation process. As renewable energy projects continue to expand worldwide, solutions like these play a vital role in building a more sustainable and resilient future.