Bolt Torque

Torque, also called moment of force, is a rotational moment. It is a measure of how much twisting is applied to tighten (turn) the nut on a bolt.  When bolting flanges together or anything else tor that matter, tightening the nut stretches the bolt adding pressure to the gasket.  The bolt are designed to stretch a bit acting like a spring.  Different factors can affect the torque like number of threads, oil, rust, type of material, etc.

 

Bolt Torque formula
\(\large{ T = \frac {k\;d\;p} {12}  }\)
Symbol	English	Metric
\(\large{ T }\) = torque	\(\large{lbf-ft}\)	\(\large{N-m}\)
\(\large{ p }\) = desired clamp load tension	\(\large{lbf}\)	\(\large{N}\)
\(\large{ d }\) = nominal diameter	\(\large{in}\)	\(\large{mm}\)
\(\large{ k }\) = torque coefficient	\(\large{dimensionless}\)