NR NR/L3/SIG/11303/1H25 ISSUE 2 PDF

Introduction

In certain instances, equipment is liable to be distorted or damaged if bolted connections are done up too tightly. In such cases, a torque wrench is used to check that the force applied to tighten the nut is limited to that which is specified. A torque wrench is also used to check that a nut is sufficiently tightened to give adequate clamping or security for the job it has to do.

Individual installation instructions in this handbook will specify where a torque wrench is to be used and what torque is required. Note that this is the figure to which the torque wrench should be set with reasonable visual accuracy; it is not a measure that has to be obtained to a very close tolerance.

Most of the applied torque is used up in overcoming friction: at the bearing face of the nut and between the mating threads. Only about 10% of the torque is used in applying an axial load to the bolt. You should therefore use only clean and undamaged nuts, bolts, and washers as dirt or damage will greatly affect the friction and thus alter the desired load in the bolt.

Where instructions require the use of a torque wrench, it is essential that a suitable type of torque wrench, fitted with the correct socket, is used.