Torque vs. Tension: A Practical Guide to Selecting the Right Bolting Technology

Introduction

In industrial applications, the integrity of a bolted joint is often the key factor that determines whether seamless operation or catastrophic failure occurs. From pipeline flanges to critical machinery and structural steel, ensuring that bolts achieve the correct clamping force—or preload—is essential for safety and reliability.

For decades, the primary method for this was applying torque. However, a more precise method, bolt tensioning, has become the standard for many critical applications. Understanding the difference between these two technologies is key to selecting the proper process for your project. So, when should you use a hydraulic torque wrench, and when is a bolt tensioner the superior choice?

Understanding Torque: The Rotational Force

Applying torque is the most common method of tightening a bolt. A hydraulic torque wrench, like those from industry-leader PSTC -granted solutions, applies a controlled rotational force to the nut, stretching the bolt and creating the desired clamping force.

How it Works: Torque creates bolt elongation (stretch) as a result of overcoming friction—primarily under the nut face and in the threads.

Advantages:

• Versatility & Speed: Torque wrenches are fast, versatile, and can be used on almost any type of bolted joint.
• Accessibility: Tools are widely available and can be used in spaces with limited overhead clearance.
• Cost-Effective: For standard applications, hydraulic torque equipment is generally less expensive than tensioning equipment.

Disadvantages:

• Friction Dependency: The major drawback is friction. As much as 90% of the applied torque can be lost to overcoming friction, with only 10% contributing to useful bolt stretch. This friction is unpredictable and can vary wildly depending on lubrication, surface finish, and thread condition.
• Inaccurate Preload: Due to the unpredictable nature of friction, the final bolt preload achieved through torque can have a wide scatter, often varying by as much as ±30%.

Best For: General engineering applications, structural steel, and situations where speed is critical, and the absolute precision of bolt preload is secondary.

Understanding Tension: The Axial Stretch

Bolt tensioning is a more advanced and accurate method. Instead of turning the nut, a hydraulic tensioner grips the end of the bolt and stretches it axially (like a highly-controlled rubber band). The nut is then turned down by hand to lock in that stretch.

How it Works: The tensioner directly applies the desired preload by stretching the bolt before the nut is tightened. Friction is eliminated from the equation.

Advantages:

• Extreme Accuracy: Because friction is not a factor, tensioning achieves a highly accurate and uniform bolt preload, typically within ±10%.
• Uniform Gasket Compression: Multiple tensioners can be linked together to tighten several bolts on a flange simultaneously, ensuring even gasket compression and a high-integrity, leak-free seal.
• Increased Safety & Speed on Critical Flanges: Eliminates the risk of galling and reduces the time required for tightening large, multi-bolt flanges.

Disadvantages:

• Requires More Access: Tensioners require extra bolt length protruding above the nut to grip onto, and more radial clearance around the nut.
• More Specialized: The equipment is more application-specific than a universal torque wrench.

Best For: Critical applications where preload accuracy is paramount, such as pressure vessel flanges, pipeline flanges, engine components, and foundation bolts.

Making the Right Choice for Your Application

The Right Tool for Every Critical Job

At Pressure Systems KSA, we believe in a customized approach, tailored to each individual’s needs. As a supplier of premier PSTC -granted solutions equipment, we provide both best-in-class hydraulic torque wrenches and advanced bolt tensioning systems.

Our role is to act as your technical partner, helping you analyze your application to determine the most effective, safe, and accurate bolting technology for the job. We provide not just the tools, but the expertise to ensure your critical joints are secured right the first time.

Have a critical bolting application? Contact the PSTC team today to discuss whether torque or tension is the right solution for you.