What Is a Kelly Bar?

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Kelly bars (also called grief joints, kelly joints and kelly stems) are used during the execution of boreholes by hydraulic rotary drilling rigs. The bars themselves are hollow and attach to the top of the drill column. Kelly bars operate by transferring the torque and crowd force from a rotary drive tool to the drilling tool. Many kelly bars can be applied to any type of piling rig that is available on the market.


Foundation Equpment


Kelly bars can be divided into two main types: friction kelly bars and interlocking kelly bars. Friction kelly bars are named such due to the frictional contact created between the rails of each element. Interlocking kelly bars, on the other hand, do not have frictional contact between the rails of each element, but instead have drive ribs that are welded with lock devices in order to transfer the maximum amount of torque to each scope. Standard kelly bars are manufactured to be fully lockable systems with a mechanical locking mechanism between each element and the outer bar and rotary drive.


Kelly bars can come with several additional standard features, including:

  • 2-element to 6-element telescopic kelly bars for piling

  • A depth range of 10m to 110m

  • Torque transfer capacity of 80kNm to 500kNm

  • Both interlocking and friction kelly bars

  • High quality seamless steel pipes

  • 6 cams and drive ribs

  • A top flange used to connect the kelly bar to a kelly swivel

  • Upper and/or lower spring shock absorbers

  • A square kelly box for connection the drilling tools

  • A drive pipe to transfer the torque and crowd force to the kelly bar


When purchasing a kelly bar for a drill rig, it's important to look for bars made of high-quality steel with strong mechanical features. No matter whether buying kelly bars new or used, it's also good to look for bars that include origin and quality certificates to guarantee their reliability and longevity. All kelly bars can be purchased with a damping noise system, which can help to reduce the disruptive, high-frequency noises produced during operation; a damping noise system comprises of a phono-absorbent material applied to the outer scope of the kelly bar, which is protected by a steel plates.


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