Drilling collar / drilling pipes / unions/cross/kelly chokes/pup joints

 A component of a drillstring that provides weight on the bit for drilling. Drill collars are thick-walled tubular pieces machined from solid bars of steel, usually plain carbon steel but sometimes of nonmagnetic nickel-copper alloy or other nonmagnetic premium alloys.

The bars of steel are drilled from end to end to provide a passage to pumping drilling fluids through the collars. The outside diameter of the steel bars may be machined slightly to ensure roundness, and in some cases may be machined with helical grooves (“spiral collars”).


The difference between drill pipe and drill collar

The drill collar is located at the lower part of the drill string and is the main component of the lower drill assembly. Its main feature is that the wall thickness is large (generally 38~53mm, which is equivalent to 4~6 times the wall thickness of the drill pipe), and it has greater gravity and rigidity. Drill collars are generally divided into 3 types: auger collars, non-magnetic drill collars, and integral drill collars.

Drill pipe is a steel pipe with a thread at the end, which is used to connect the surface equipment of the drilling rig and the drilling and grinding equipment or bottom hole device at the bottom of the well. The purpose of the drill pipe is to transport the drilling mud to the drill bit and together with the drill bit raise, lower or rotate the bottom hole device.

Difference: The drill collar is thicker than the drill pipe wall, and the weight per unit length is heavier. The lower part of the drill collar is connected with the drill bit, and the upper part is connected with the drill pipe. The functions are similar. The drill pipe mainly transmits motion and power. The drill collar is stronger than the drill pipe and directly drives the drill bit to work.

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