Drillrods vary in terms of thread design and material dimensions based on their intended application but all share the same essential functions the most important of which are:
- They transmit rotary torque and rotational speed (power) to the drill bit.
- They transmit the flushing medium (air or water or mud) to the bit.
- They act as a link between the drill bit and the thrust control system of the drill rig.
- They allow removal of worn drill bits and reinsertion of new drill bits.
In recent years the requirement for deeper cored boreholes has necessitated that exploration drilling contractors drill close to or beyond the safe working limit of the drillrods in use. This significantly increases the risk of catastrophic failures and so a deeper appreciation of the mechanical properties, design parameters and therefore the depth limitations of commonly used diamond drilling rods is very important.
This paper aims to briefly outline some of the more important issues involved in the design, manufacture and use of drillrods. While this paper is focused on diamond core drillrod the principles discussed apply to all drillrod / drillpipe used in other drilling applications.