Tightening of non-preloaded bolts
Customers very often asking for torque figures for installation of non-preloaded bolt assemblies. Due to nature of this type of product, assemblies for non-preload connections, there are no torque figures available.
There are various guidances available to calculate theoretical torque figures, but following EN 1090-2 (pt. 8.3), tightening of non-preloaded bolts shall be conducted as follow:
The connected components shall be drawn together such that they archive firm contact. Shims may be used to adjust the fit. (…)
Each bolt assembly shall be brought at least to a snug-tight condition, with special care being given to avoid over-tightening especially short bolts and M12. The tightening process shall be carried out from bolt to bolt of the group, starting from the most rigid part of the connection and moving progressively towards the least rigid part. To archive a uniform snug-tight condition, more than one cycle of tightening may be necessary.
NOTE 1 (…)
NOTE 2 The term “snug-tight” can generally be taken as the achievable by the effort of one man using a normal sized spanner without an extension arm, and can be set as the point at which a percussion wrench starts hammering.
For more details please refer to a full version of the standard.