What is the difference between preloaded and non-preloaded bolting assemblies?

Apart from dimensional differences (bigger heads of bolts and bigger nuts on preloaded assemblies), the main difference is in the way how these goods are installed.

Non-preloaded bolting assemblies are generally tightened to at least snug-tight. The connected components are drawn together to achieve firm contact without any specific preload.

The “snug-tight” is generally referenced as tightening the assembly by one man using a normal-sized spanner without an extension arm until the wrench starts hammering.

See more: Tightening of non-preloaded bolts

Preloaded bolting assemblies are tightened to at least a minimum specified force (preload). The tightening is carried out according to specified installation methods (with DTI washers, using combined method, torque figures or tension controlled). This type of product is generally used for critical, slip-resistant, seismic connections, fatigue resistance, execution purposes or as a quality measure (for example: for durability).

Preloaded bolting assemblies can be used as non-preloaded bolting assemblies, where non-preloaded shall not be preloaded unless specified by the construction engineer.

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