How Bolt Tensioning Works
Strong bolted joints are crucial in demanding fields like power plants, oil and gas refineries, and major construction projects. When bolts are loose or not tightened correctly, they can significantly weaken the equipment and threaten its safety and reliability. This can lead to expensive shutdowns and even pose safety risks.
Bolt tensioning offers a dependable solution to create secure, leak-proof bolted connections. These connections can endure harsh operating conditions and maintain their tightness over time.
Below, we explain how bolt tensioning works by differentiating between torque and bolt tensioning, looking at the bolt tensioning process, and exploring its advantages for various industries
Traditional Torque vs. Bolt Tensioning
Torque
Traditionally, technicians used manual or hydraulic torque wrenches to tighten bolts. These wrenches work by applying a twisting force to the nut or bolt head. This force creates tension within the bolt by using friction between the threads and the connected surfaces. However, this approach has several inherent limitations:
- Torque can be imprecise – The actual tightness of the bolt (clamping force) depends on several factors, such as friction, surface condition, and lubrication. These can vary greatly between situations, making it difficult to get the exact tightness needed.
- Tightness can loosen over time – Bolts experience heat changes, vibrations, and other stresses during use. Even if they’re tightened properly at first, the tightness (preload) can decrease over time, leading to leaks and even joint failure.
Bolt Tensioning
In comparison, bolt tensioning provides a more reliable way to achieve the exact tightness needed in bolted joints. Instead of relying on friction, which can be unpredictable, bolt tensioners pull or stretch the stud directly.
This stretching, within safe limits, creates a specific clamping force across the entire joint. This force is directly measured, so you know exactly how tight the joint is, regardless of friction between surfaces.
How Hydraulic Bolt Tensioning Works: A Step-by-Step Breakdown
Bolt tensioning is a more accurate method for securing bolted joints and determining bolt load. The process typically involves the following steps:
1. Position the Bolt Tensioner
A hydraulic bolt tensioner is positioned over the bolt or stud with the tool’s piston or tensioning cylinder making contact with the bolt or nut.
2. Apply Hydraulic Pressure
Hydraulic pressure is applied to the tensioner, stretching the bolt or stud until it comes into contact with the flange face or joint surface.
3. Monitor Elongation
As the hydraulic pressure increases, the bolt’s elongation is carefully monitored to ensure the correct preload is achieved.
4. Tighten the Remaining Bolts
Once the first bolt or stud is tensioned, the process is repeated for the remaining bolts or studs, ensuring that all bolts are tensioned simultaneously to the required load.
5. Release the Hydraulic Pressure
After all bolts are tensioned, the hydraulic pressure is gradually released, allowing the stretched bolts to try to return to their original length. This creates a continuous clamping force across the joint, counteracting the effects of load loss and maintaining the preload over time.
This process ensures that all the bolts in a joint are pre-loaded to the exact tension needed for the particular application.
Advantages of Bolt Tensioning
Several advantages make bolt tensioning the preferred choice for critical bolting tasks:
- Accurate and consistent preload – Unlike torque wrenches that rely on friction, bolt tensioning applies a direct pulling force, stretching the bolt to a precise length. This ensures all the bolts in a joint have the exact tightness needed, regardless of surface conditions.
- Maintained preload over time – Even after exposure to heat, vibrations, and other stresses, the stretched bolts maintain their clamping force, keeping the joint secure over its entire lifespan.
- Uniform gasket compression – By tightening all the bolts at once, bolt tensioning creates a uniform pressure on the gasket between the connected parts. This reduces the risk of leaks and joint failure.
- Reduced risk of hand injuries – Traditional methods using high torque wrenches can cause hand injuries. Bolt tensioning applies a controlled pulling force, minimizing this risk.
- Increased productivity – The ability to tighten multiple bolts simultaneously makes bolt tensioning a faster and more efficient way to complete critical bolting tasks.
Applications for Bolt Tensioning
Bolt tensioning finds application in various industries, including:
- Oil and gas – Ensuring secure connections in pipelines, refineries, and other critical infrastructure.
- Wind energy – Maintaining the integrity of wind turbine towers and blade connections.
- Petrochemical – Guaranteeing leak-proof connections in processing equipment and vessels.
- Construction – Securing high-strength joints in bridges, buildings, and other structures.
Let ALLTORC Keep Your Applications Bolted Down
Bolt tensioning is a critical process for ensuring the safety and reliability of bolted connections in demanding industrial applications. By stretching the bolt within its elastic limit and creating a precise clamping force, bolt tensioning overcomes the limitations of traditional torquing methods, providing consistent preload, uniform gasket compression, and maintained joint integrity over time.
As a trusted partner, ALLTORC Bolting Solutions is committed to providing the highest quality bolt tensioning tools, equipment, expert guidance, and support to help you achieve reliable and long-lasting bolted connections.