Understanding of Torque Tightening and Its Associated Terms

In many of the mechanical operations, often toque tightening is needed for tightening the flanges to avoid any leakage of fluid. Let us get familiar with this process.

  • Torque tightening

If any fluid is involved then it will need leak-free flange connection. In order to prevent leakage of fluid, installation of proper gasket is required and the bolts used for this purpose must have correct amount of tension and also the strength of the bolt must be suitably divided over the face of the while flange. The correct bolt tension can be achieved with torque tightening.


When we talk about proper tightening of bolt then it means that we need to make best use of elastic property of the bolt. Therefore, for proper working of the bolt it must work like a spring. In actual operation, in the process of tightening, an axial pre-load tension is exerted on the bolt. The tension load that is applied is equal and opposite to the force applied by compression on the components to be assembled. This process is also known as “tension load or “tightening load” and flange spreader has got no role in it.

  • Torque wrench

Torque wrench is nothing but a hand-guided tool for screwing and its use is to set the amount of force to tighten a fastener like nut or bolt. Here, the torque wrench operator can know how much rotational force or torque has been applied to the bolt so that he can tighten the nut or the bolt.

The technique for proper flange bolt tightening needs little experience of this operation. The operation can be successful if the operator has sufficient experience about the tightening technique and also the right kind of tool is used for the operation. Following tools are generally used for flange bolt tightening:

  1. Impact wrench
  2. Manual wrench
  3. Hammer wrench
  4. Hydraulic bolt tensioner
  5. Hydraulic torque wrench
  6. Gear assisted torque wrench

  • Torque loss

There will be certain amount of torque loss in any kind of bolted joint. Various things are responsible for torque loss and they are:

  1. Gasket creep
  2. Effects of bolt relaxation
  3. Thermal expansion
  4. Vibration in the system
  5. During bolt tightening the elastic interaction

In order to reduce the torque loss, proper gasket installation is necessary. Proper thickness of the gasket also need to be considered for reducing torque loss. If the gasket is thicker then it can result into torque loss. With thinner gasket material it can take higher gasket load and hence higher internal pressure.