Sucker Rod Centralizer Torque Transmission Design
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Solution Overview
Problem
In high torque applications for sucker rod strings in oil wells, existing centralizer designs fail to prevent wear on the tubing wall due to inadequate bearing contact surface, leading to premature failure and damage.
Innovation Solution
A coupling assembly with a mandrel and rotor design featuring undercuts or threaded nuts, where the outer diameters of the stops are equal to or less than the couplings, and a tubular body with raised fins, allowing for increased bearing surface contact and torque transmission without material yield, and a self-locking nut design to secure the rotor axially.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the bearing contact surface between the mandrel and couplings is increased to transmit higher torque, then torque transmission capability is improved, but the shoulder area that fixes the soft non-metallic centralizer decreases resulting in premature failure and axial travel of the rotor
Solution Approach 1:
The mandrel is divided into multiple components: a shaft portion, a nut portion, and a shoulder portion. This segmentation allows each component to perform its specific function - the shaft provides bearing surface for torque transmission, the nut secures the rotor axially, and the shoulder provides additional fixation area, thereby resolving the contradiction between torque transmission and centralizer stability
Solution Approach 2:
The self-locking nut acts as an intermediary element between the mandrel and the rotor. It provides axial securing of the rotor while allowing the mandrel shaft to maintain its bearing contact surface for torque transmission, thus mediating between the conflicting requirements of torque transmission and rotor fixation
2Ease of manufacture
If a standard one-piece centralizer design is used, then manufacturing is simpler, but the bearing contact surface is insufficient for high torque applications leading to material failure
Solution Approach 1:
The mandrel is segmented into a shaft portion, nut portion, and shoulder portion that can be manufactured separately and then assembled. This allows each component to be optimized for its specific function while maintaining manufacturing feasibility, resolving the contradiction between manufacturing simplicity and torque transmission strength
Solution Approach 2:
The centralizer assembly uses composite construction combining metallic components (mandrel shaft, nut, shoulder) with a soft non-metallic rotor. This composite approach allows the metallic parts to handle high torque loads while the soft rotor provides centralizing function and protects the tubing wall, resolving the strength limitation of one-piece designs
3Power
If the outer diameter of the mandrel is increased to provide greater bearing contact surface, then torque transmission is improved, but the shoulder area for fixing the rotor decreases
Solution Approach 1:
The mandrel is segmented into distinct functional portions: the shaft portion with optimized diameter for bearing contact and torque transmission, and the shoulder portion that provides fixation area. This segmentation allows independent optimization of each portion's dimensions, resolving the contradiction between bearing surface area and shoulder fixation area
Solution Approach 2:
The solution adds the nut portion as a separate axial element that provides fixation without consuming radial dimension. This dimensional approach allows the shaft to maintain its torque-transmitting diameter while the nut provides additional axial securing, effectively adding a new dimension to the fixation mechanism
Data Source
AI summary
A coupling assembly is disclosed for connecting and centralizing a first threaded-end member and a second threaded-end member, the coupling assembly comprising: a mandrel having a rotor receiving surface bounded by a first stop and a second stop, the mandrel having a first threaded pin at a first end for connection to a first threaded box coupling for the first threaded-end member, and a second threaded pin at a second end for connection to a second threaded box coupling for the second threaded-end member; each of the first stop and the second stop having respective outer diameters and the respective outer diameters being less than or equal to the respective outer diameters of the first threaded box coupling and the second respective box coupling; and a rotor with raised fins mounted on the rotor receiving surface between the first stop and the second stop.