The University of Drilling is a practical learning site, not an accredited school.

Kelly Arrangements

Various aspects of a Kelly, Kelly Bushing and Rotary Table.
Rollers of a kelly bushing
View of the rollers on a Kelly Burhing.
Features of a Drilling Kelly

A kelly is a square or hexagonal shaped steel pipe connecting the swivel to the drill pipe. The kelly moves through the rotary table and transmits torque to the drill strong (see API RP 54).


Rotation is transferred to the kelly and connected drill string through a special device called the kelly bushing, which when fitted into the master bushing transmits torque to the kelly and simultaneously permits vertical movement of the kelly to make hole.  The kelly bushing can be shaped to fit the rotary opening or have pins for transmitting torque.  A kelly bushing may also be called the drive bushing.

Vertical movement of the kelly during rotation is facilitated by rollers in the kelly bushing that engage and turn the square or hexagonal sides passing through the kelly bushing and roll to allow axial motion when turning to the right or drilling.

A kelly saver sub is connected between the kelly and the drill pipe of the drill string to protect the kelly from wear during make-up and break-out of the threaded connections.  A rubber protector also forms part of the kelly saver sub to cushion any adverse rotation of the kelly during rotation.

Kelly Saver Sub with a Protector
Aspects of a kelly valve.

A kelly cock is a valve immediately above the kelly that can be closed to confine pressures

inside the drill string while a lower kelly valve is essentially a full-opening valve installed immediately below the kelly, with outside diameter equal to the tool joint outside diameter. Valve can be closed to

remove the kelly under pressure and can be stripped in the hole for snubbing operations. (See API RP 53)