Importance

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Abstract

An elongated drive string assembly comprising a plurality of hollow sucker rods and connecting elements with an axis, connected together and between a drive head located at the surface of an oil well and a rotary pump located deep down hole in an oil well. Each hollow sucker rod has at least a first end comprising an internal female threaded surface engaging an external male threaded surface on a connecting element, such as a nipple. In order to further optimize the stress distribution between the elements, frustro-conical, non-symmetrical threads with a differential diametral taper are used. Preferably two torque shoulders with a maximized mean diameter and cross-sectional area are used to resist storing reactive torque in the drive string. The nipple free end defines a second torque shoulder that adds to the torque transmission during make-up while also defining a small seal at that free end to decrease corrosion erosion problems. This overall configuration ensures high yield torque, high shear strength, lowered stress concentration and a surprising resistance to storing reactive torque, which minimizes dangerous backspin when power to the sucker rod string is interrupted.

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First Claim