Round drilling collar

The drill collar is one of the main components of the drill string. Its function is to provide the bit with WOB, and at the same time make the BHA have greater rigidity, so that the bit can work stably and help to overcome the problem of deviation. Sanjack can provide drilling collars with various types to fit different environment and applications. All drill collars are manufactured in accordance with national standards as applicable.

Round drill collars are slick thick-walled round pipes with integral structure, so also called integral drill collars or slick drill collars. The thickness ranges generally 38-53mm, which is more than four times that of conventional drill pipes. They have greater strength and rigidity

Since the weight on bit is formed by the weight of the drill string, the lower part of the drill string is subject to compressive stress. When drilling, the WOB value is generally greater than the critical value of the pressure bar stability of the drill string, so the drill string at the lower pressure part will bend under its own weight. When the bent drill string rotates, it will cause alternating stress, which will lead to fatigue failure of the drill string. In order to reduce the degree of fatigue failure, the bending stress should be reduced. This requires shortening the length of the compression section and increasing its rigidity. Therefore, drill collars are used instead of drill rods at the lower end of the drill string.

Basic Structure

For drilling collars, joints are directly turned on both ends of the pipe body without additional joints


OD range Yield strength Tensile strength Elongation Hardness Charpy impact energy
mm in MPa MPa % HB J
79.4~171.4 3 1/8~    6 3/4 ≥788 ≥1005 ≥13 295~341 ≥70J
177.8~279.4 7~11 ≥719 ≥960 ≥13 295~341 ≥70J

1) Apply WOB to the bit

2) Keep the drill pipe in tension and ensure the strength of the drill pipe under compression

3) Reduce the vibration, jump and swing of the drill bit to make it work smoothly

4) Controlling well deviation

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