Tightening Methods

Torque Controlled Tightening

By using manual, pneumatic or hydraulic torque wrenches, it is possible to tighten flanged joints with tie rods of any diameter.

The use of the hydraulic torque wrench represents a simple and reliable solution for tightening flanged couplings; the control of the tightening torque allows, in fact, to supply the tie rods with the required load with a good approximation (± 10%).

Depending on the model chosen, the wrenches develop a torque of between 200 Nm, ideal for providing “correct” stress to the tie rod in the event that, for example, it is important not to exceed certain load values on the gasket, up to 35000 Nm, a value sufficient to supply a tension of 300 N / mm2 for 4 ”tie rods.

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Controlled Load Tightening

Available in a wide range of models for tie rods up to 6 ”, they are capable of developing a maximum load of 5,000 kN.

The tensioner consists of an annular piston interposed between a threaded insert, screwed to the end of the tie rod, and a support bridge, equipped with a drain on the base to allow access to the nut with a maneuver pin.

The traction applied directly to the tie rod extends it, making it possible to rotate the nut by hand by means of a rod to be inserted on the holes made on the faces of the nut itself, or, if this does not have one, on the holes of the external crown of a special hexagonal bush.

For the application of the hydraulic tensioners it is necessary that each tie rod protrudes from the nut by a length equal at least once its diameter.

It is advisable to tension at least 4 tie rods at the same time, in order to uniformly compress the gasket avoiding load asymmetries and consequent stress phenomena.

The method is extremely accurate (± 5%) because it is independent of the friction and torsional stresses found in traditional torque tightening systems.

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Control of the elongation of the tie rods

The control of the load with an ultrasound system, associated with both tightening with a torque wrench and with direct tensioning, serves to verify that the residual tension on the tie rod corresponds to the theoretical value required.

This measurement is generally carried out with an ultrasound system, whose operating principle is based on the measurement of the time taken by a shock wave to travel the entire length of the tie rod; from this measurement, carried out before and after tensioning, it is possible to trace the elongation suffered by the tie rod and therefore the tension applied to it.