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In this article, we'll explain the concepts of bolt tensioning how a bolt can be stretched and why you would choose to tension a bolt.

What is bolt tensioning?

Tensioning is a controlled way of tightening a bolt on applications within critical industries such as oil and gas, wind energy, construction and nuclear etc.

This is done by stretching the bolt to the initial load. The nut is then rotated onto the flange face which keeps the load in the bolt once it has relaxed. 

How can bolt stretch?

Most materials have what we call an elastic region. This is where the material when put under tensile stress will go back to its original state once the stress has been removed.

If a material is put under too much tensile stress, then it will enter the plastic region which is the point of no return and where the material can no longer revert to its original form. This is the same case for metal.

Hydraulics are used to pressurize the tool which then transfers the pressure energy into tensile stress on the stud. When designing a tensioning tool, calculations are made based on the stud’s material specification to make sure the stress is not too great that it will damage the stud.

The first signs of damage is what is called necking. This is when the stud starts to deform and beyond this point, the stud will then break.

Why choose tensioning?

So, the main benefits of tensioning are that tools can achieve extremely high loads. The process can be quicker by one operator using multiple tools simultaneously, it is very accurate the tools are extremely durable, and it can be used in multiple environments. Topside in extreme temperatures, and subsea at greater depths.

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