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Holding it together – bolting solutions for safety critical environments

07 August 2019

It is an exciting time to be working in nuclear engineering, with around 60 reactors currently under construction. In boosting capacity to meet global energy demand, the sector has to face the challenge of increasing supply without compromising safety. As infrastructure projects become more ambitious and complex, structural integrity is of paramount concern, and key to this is the joints which literally hold these structures together. As the nuclear industry enters its next stage of growth, more efficient bolting solutions will become ever more important in reducing exposure.

Whether it be constructing new nuclear power plants, or extending the life of existing reactors, safety is always the overriding concern. These super structures have to withstand enormous pressures, which means that engineers are continually searching for ways to make them not only easier to build, refuel and maintain, but also shows a drive for improvement whilst maintaining robust and reliable standards as the basic design criteria.

Creating tension and maintaining it through the myriad of bolted joints within these structures is one of their greatest challenges. Not only must the bolts themselves be of the highest quality, but engineers need to access reliable and highly efficient tools to ensure that bolts are correctly tensioned within the specified residual bolt load tolerances.

Since the development of its wedge-locking technology in 1982, Nord-Lock Group has supplied the power generation sector with a range of innovative bolting solutions. Be it Superbolt mechanical tensioners, Boltight hydraulic tensioners, or Expander System pivot pins, the Swedish group has been at the forefront of secure bolting solutions.

Superbolt’s revolutionary multi-jackbolt tensioning (MJT) technology has been used on multiple nuclear installations, solving complex bolting challenges. The company’s MJTs take high preloads and break them down into manageable torques using the jackbolts threaded through the nut body. Joints can be tightened with high accuracy without requiring specialized skills or heavy tooling.

Superbolt products are ideal for use within nuclear projects and on structures where there is a mixture of bolting complexity and extreme requirements. This means the need for precise material properties, meeting extreme bolt loads, working within limited spaces, and coping with a wide range of temperatures.

The technology keeps evolving to meet the needs of power generation engineers. At ITER Business Forum 2019, Superbolt launched a ground-breaking product which allows high-volume users of its MJTs to tighten all jackbolts simultaneously. This reduces installation and removal times considerably, helping to improve maintenance planning to minimise exposure and help maximise revenue.

The nuclear industry is also benefiting from the use of hydraulic bolt tensioning technology to raise safety standards. These tools guarantee accurate and easy tightening of bolts to the correct preloads. The method is far more reliable than conventional tightening solutions and does not use torque or any forceful turning. Hydraulic tensioning has been a recognised standard in the nuclear industry for many years for RPVH, SG Manways and RCP applications and is constantly adapted to more critical applications such as Safety and MSI Valves.

Other methods cause friction, which uses up around 80% of the torque energy applied to the bolt. Instead, this approach applies tension directly to stretch the bolt. It applies a consistent force, meaning the applied load can be controlled far more accurately. The hydraulically applied load can be simultaneously applied to give uniform residual bolt load. Even joint and gasket compression ensure leak-free service achieved quickly, further reducing exposure times.

Project engineers understand how integral bolts are to the integrity of a structure. Securing bolts with quality washers for optimum load distribution and using reliable tools used to ensure bolts are at the right residual load is safety critical. Without these measures in place, structural integrity
is compromised and the results can be catastrophic.


Keeping pace

As part of the Nord-Lock Group, Boltight’s hydraulic tensioning and Superbolt’s mechanical tensioning solutions are evolving fast to meet the changing needs of its customers. Innovation is key to that endeavour and the company has embraced digitisation by introducing augmented reality (AR). Products are brought to 3D life by an innovative AR experience which provides customers with an exploded view of their products.

The user can view the virtual products, rotate and explode and place onto a virtual flange. With links literature, videos and the website, the experiences give all the information customers need to understand how the products work.

Nuclear power generation is set to grow at a rapid rate. According to the World Nuclear Association, nuclear energy now provides about 11% of the world's electricity from about 450 power reactors. In the future, nuclear will be a key source of low-carbon power.

The association’s Harmony programme proposes the addition of 1000 GWe of new nuclear capacity by 2050, to provide 25% of our electricity. The industry is already responding with an ambitious investment drive. Over 100 power reactors with a total gross capacity of about 120,000 MW are on order or planned, and a further 300 or more have been proposed. 

The challenge now is to ensure innovations in design and technology keep pace with demand. How do you ensure structural integrity as well as upholding safety standards? The answer lies in innovation, investing in R&D and forming long-term partnerships with manufacturers who share your vision.

Whatever tomorrow might have in store for the global energy sector, that collaborative approach is what will turn concepts into workable projects and overcome technical difficulties with the smartest of solutions.

West Midlands manufacturer Boltight has almost 20 years’ experience manufacturing hydraulic bolt tensioning systems used within extreme and hazardous environments around the globe.

Its tools and auxiliary equipment are used for numerous bolting applications within nuclear power stations, including pressure vessel covers, steam generators, manways and handholes, access points and pumps.