Holding it together

Creating tension and maintaining it through the myriad of bolted joints within nuclear plant structures is a challenge. Not only must the bolts themselves be of the highest quality, but engineers need reliable and efficient tools to ensure that bolts are correctly tensioned and within the specified residual bolt load tolerances.

Multi-jackbolt tensioning (MJT) has been used on several nuclear installations. MJTs take high preloads and break them down into manageable torques, using the jackbolts threaded through the nut body. Joints can therefore be tightened with high accuracy without requiring special skills or heavy tooling.

The technology keeps evolving to meet the needs of power generation engineers. At the ITER Business Forum 2019, Superbolt (part of the Nord-Lock Group) launched a new product that allows high-volume users of its MJTs to tighten all jackbolts simultaneously. This reduces installation and removal times considerably, helping maintenance planning, minimising exposure and maximising revenue.

The nuclear industry is also benefiting from the use of hydraulic bolt tensioning 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 and does not use torque or any forceful turning. Hydraulic tensioning has been a recognised standard in the nuclear industry for many years for reactor pressure vessel heads, steam generator manways and reactor cooling pump applications and has been adapted to other critical applications such as safety and main steam isolation 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, so 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 is 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 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.

As part of the Nord-Lock Group, Boltight’s hydraulic tensioning and Superbolt’s mechanical tensioning solutions are evolving to meet the changing needs of its customers. Innovation is key to that endeavour and the company has embraced digitisation. By introducing augmented reality products are brought to 3D life and customers can see an exploded view of the products.

The user can view the virtual products, rotate and explode, and place onto a virtual flange.

The challenge now is to ensure 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.

That collaborative approach is what will turn concepts into workable projects and overcome technical difficulties with the smartest of solutions.