The rotary table is a rotating device that is mostly used in drilling rigs to provide clockwise rotational force to the drill string. This is primarily used to facilitate the process of drilling a borehole. The rotary speed can also be called as its rpm – the number of rotations performed in a minute. Rotary tables are also commonly referred to as ‘turntables’ in the industry.
Most rotary tables use chain–driven mechanisms. The function and movement of the chain resemble that of a bicycle chain assembly. The chain requires frequent lubrication to avoid seizing and burning. Most of the rotary tables also include a rotary lock. The lock is installed to allow the table to be moved in a fixed direction. It can also be unlocked to free it from restrictions, allowing the rotary table to be moved in both directions. This feature is often used by crews instead of using a second pair of tongs for making up or breaking out pipes.
The rotary bushings are installed at the center of the rotary table. These bushings can also be removed in two separate pieces to allow large items such as drill bits to pass through the rotary table. The large gap at the center of the rotary table is referred to as the ‘bowl’ because of its shape and appearance. Slips are set in the bowl to hold up the drill string during connections and pipe trips along with the point where the drill string passes through the floor into the wellbore. The rotary bushings connect to the kelly bushings to induce the spin the required for the drilling.
Of late, drilling rigs rarely feature rotary drives. The modern rigs use top-drive technology where the drill string is turned by the mechanisms located at the top of the string. The top drive is attached to the blocks. In this process, the swivel is not required because all the necessary actions are performed by the top drive itself. However, the top drive has not eliminated the use of kelly bar and kelly bushings.