Comparison of common bolt tightening methods
Proper preloading of a bolted connection is a difficult task. Therefore, several different tightening methods were developed – each with their specific advantages and disadvantages. So, different methods are preferred in different industries or for certain applications.
Generally, tightening methods can be categorised according to the principle of how the preload is generated. There are 2 basic principles:
- Rotational tightening (torque controlled, angle controlled, yield controlled), where the tensioner is rotated to directly produce the preload.
- Tensioning (hydraulic, thermal, mechanical), where the bolt is stretched without rotating the tensioner, typically by means of an external power supply.
For large boltings, especially for large sizes above M39 or 1.5”, the three tightening methods shown below are predominant. This comparison is based solely on the indisputable physics behind these methods and illustrated with the help of Roetscher’s diagram.