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Drill collar is seated between drill bit and dill pipe or drill bit and heavy weight drill pipe. It is mainly used to provide bit pressure for drill bit and control well deflection. It is usually use high-grade alloy steel as material. Now in China there are also collars using rolled steel bars as material, made by heat treatment machining. Wall thickness of these collars are 4 or 6 times of drill pipe,having large stiff.
Drill collar
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