What is the Difference Between Bolt Tensioning and Bolt Torquing?
Properly tightened bolts are critical in assorted industries to ensure the integrity and safety of equipment and structures. This includes aerospace, mining, power generation, and oil and gas. Two widely accepted methods for achieving a securely bolted joint are bolt torquing and bolt tensioning.
While both techniques aim to create a tight joint by leveraging the bolt’s elastic properties, they have distinct differences, advantages, and disadvantages that make them suitable for various applications.
Bolt Torquing vs Bolt Tensioning: An Overview
Feature | Bolt Torquing | Bolt Tensioning |
Method | Applies turning force for nut rotation and clamping | Applies direct axial load for stretch and clamping |
Application | Suitable for most general applications | Ideal for high-pressure, critical joints |
Equipment | Torque wrench | Hydraulic bolt tensioner |
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Disadvantages |
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What is Bolt Torquing?
Bolt torquing involves using a torque wrench to apply a turning force (torque) to the nut or bolt head, causing it to rotate and tighten. The applied torque works against the friction in the bolt’s threads and under the nut face to produce a clamping force. The torque value is a measurement of the force required to turn the nut around the threads. It can be expressed as Newton-meters (Nm) or foot-pounds (ft-lb).
Torquing is the most common method for tightening bolts, as it’s relatively simple and requires minimal equipment. An operator uses a calibrated torque wrench to apply a specific torque value. This value is based on factors such as bolt diameter, material properties, and desired preload.
Advantages of Bolt Torquing
- Widely available equipment
- Simple to perform
- Suitable for most general applications
- Lower initial cost compared to tensioning
Disadvantages of Bolt Torquing
- Accuracy can be affected by friction variables (thread condition, lubrication, bolt coating, and surface condition)
- Uneven load distribution in the bolt
- Potential for bolt torsion and damage to threads
- Limited suitability for high-pressure, critical applications
What is Bolt Tensioning?
Bolt tensioning is a method that applies a direct axial load to the bolt, causing it to stretch and create a clamping force without rotating the nut. This technique uses a hydraulic bolt tensioner to apply a precise load to one end of the bolt, while a reaction nut on the opposite end creates the stretch.
The tensioning process involves several steps:
- The tensioner is fitted over the bolt and engages with the nut.
- Hydraulic pressure is applied to the tensioner, which stretches the bolt and creates a preload.
- The nut is turned by hand until it contacts the joint surface.
- The hydraulic pressure is released, transferring the load back to the flange through the nut.
Advantages of Bolt Tensioning
- Highly accurate and repeatable preload
- Consistent load distribution in the bolt
- Minimizes bolt torsion and thread damage
- Ideal for high-pressure flanges with large bolt diameters or critical joints
- Reduced bolt scatter (variation in bolt preload) compared to torquing
Disadvantages of Bolt Tensioning
- Higher initial equipment cost
- Requires skilled operators
- Limited accessibility in certain joint configurations
Which Method is Better for Your Application?
The choice between bolt torquing and bolt tensioning depends on various factors, including the specific application, joint criticality, bolt size, and available resources. In general, bolt torquing is suitable for most standard bolting applications, while bolt tensioning is preferred for high-pressure, critical joints, such as those found in subsea equipment or nuclear power plants.
It’s important to note that both methods, when performed correctly, can result in a secure and leak-free joint. The key is to follow proper procedures, use calibrated equipment, and adhere to industry standards and guidelines.
ALLTORC: Your Partner in Bolting Solutions
At ALLTORC, we understand the importance of proper bolt tightening to ensure critical equipment is safe and reliable. As a leading provider of industrial-grade torque and tension equipment, we offer a comprehensive range of solutions to meet the diverse needs of our customers.
Our product lineup includes hydraulic torque wrenches, bolt tensioners, and torque measurement tools, all designed to deliver precise and consistent results. Whether you require equipment for general bolting applications or specialized tools for high-pressure, critical joints, ALLTORC has the expertise and solutions to support your needs.
Please contact our knowledgeable team today to find out more.