- Hydraulic torque wrenches
- Pneumatic torque wrenches
- Electric torque wrenches
- Torque wrench accessories
- Manual torque multipliers
- Hydraulic bolt tensioners
- Hydraulic bolting pumps
- Flange alignment tools
- Flange puller set
- Flange facing tools
- Flange spreaders
- Valve change-out tools
- Nut cutters
What is torque?
It is the measurement of the amount of force needed to rotate an object.
What is torque tightening?
The application of a preload on a fastening element by turning the fixing nut.
The friction points should always be lubricated when using the torque tightening method.
Torque tightening and preload
The amount of preload created when tightening is largely dependent on the effects of friction.
There are three main “torque components”:
- the torque to tighten the bolt;
- the torque to overcome friction in the bolt and nut threads;
- the torque to overcome the friction on the outer side of the nut (contact surface).
** Preload (residual load) = applied torque minus friction losses **
Lubrication reduces friction
Lubrication reduces friction during tightening and reduces the risk of breakage during installation, increasing the lifespan of the bolt. The variations in the friction coefficients influence the preload obtained at a specific torque. High friction results in reduced torque to preload conversion.
The value of the friction coefficient supplied by the lubricant manufacturer must be known in order to be able to accurately establish the required torque value. Lubricants and anti-seize agents must be applied both on the sealing surface of the nut and on the thread.
This example illustrates how lubricant can reduce the effect of friction and convert more preload tension on the bolt.
The nominal values of pressure and torque, indicated by the manufacturer, correspond to the maximum safety limits. The best practice is to limit yourself to 80% of these values.
During tightening, it is common practice to only tighten one bolt at a time; this can lead to situations of load on a point or a distributed load. To avoid such situations, the bolting is carried out in stages following a predetermined order:
Step 1: Tighten with a wrench making sure 2-3 threads remain above the surface in addition to the nut.
Step 2: Tighten each bolt with a third of the required final torque following the sequence shown above.
Step 3: Increase the tightening of each bolt up to two-thirds of the final torque required following the sequence shown above.
Step 4: Increase the tightening up to the required final torque following the sequence shown above.
Step 5: Execute the final control on each bolt working clockwise starting from bolt 1 to the final torque completed.
The torque used when bolts are loosened at a higher torque than the torque normally required. It is mainly used in case of corroded and deformed nut and bolt threads.
The loosening torque cannot be calculated precisely, however, depending on the situation, it is possible to calculate up to 2½ times the input torque.
The use of penetration oils or anti-seize lubricants is always recommended when performing loosening operations.
THANKS TO THE PREPARATION AND SPECIALISATION OF OUR SIRTEC TECHNICIANS, WE ARE ABLE TO PROVIDE A CONTROLLED TORQUE TIGHTENING SERVICE, ISSUING THE RELATIVE CERTIFICATION
via Borzoli, 39
16153 GENOVA (GE) – ITALY
fax. +39 010 6505609