EN 14399-4 Torque Method

Tightening - Torque Method

The bolts shall be tightened using a torque wrench offering a suitable operating range. Hand or power operated wrenches may be used. Impact wrenches may be used for the first step of tightening for each bolt.
a) first tightening step: the wrench shall be set to a torque value of about 0.75 Mr, i with Mr, i = Mr, 2 or Mr, test. This first step shall be completed for all bolts in one connection prior to commencement of the second step.
b) a second tightening step: the wrench shall be set to a torque value of 1.10 Mr, i with Mr, i = Mr, 2 or Mr, test.

Diameter Preload [kN] Torque 1.1 Mr, i [Nm] Km
M12 59 100 0.129
M16 110 250 0.129
M20 172 450 0.119
M22 212 650 0.127
M24 247 800 0.123
M27 321 1250 0.131
M30 393 1650 0.127
M36 572 2800 0.124

Tightening torque Mr (=1.10 Mr, i) has to be applied using calibrated torque wrenches with accuracy of ± 4% According to EN ISO 6789 by rotation of the nut; different tightening procedures have to be approved by experimental tightening tests under site conditions as specified in annex H of European Standard EN 1090-2: 2008+A1:2011.