Sucker Rod Connection Fatigue Resistance via Diametrical Interference
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Solution Overview
Problem
Sucker rods, particularly 22.22 mm (⅞″) diameter, grade D, API-11B rods, fail due to high fatigue caused by lack of diametrical interference in conventional threaded connections, leading to axial tension and disengagement issues.
Innovation Solution
A tapered threaded connection with trapezoidal threads and flank-to-flank load and stab contact is introduced, providing diametrical interference to reduce axial interference and enhance fatigue resistance, featuring a shoulder perpendicular to the pin axis and another shoulder perpendicular to the box axis for controlled interference.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If conventional cylindrical threaded connection with no diametrical interference is used, then assembly is simple, but axial tension is high and fatigue resistance is poor
Solution Approach 1:
The patent changes the geometric parameters of the thread connection from cylindrical to tapered, introducing a taper angle (typically 1:16 or 1:20) to create diametrical interference. This parameter change transforms the connection from having no radial interference to having controlled radial interference, which redistributes stresses and reduces axial tension while maintaining assembly feasibility.
Solution Approach 2:
The patent introduces a radial dimension component to the thread connection by using tapered threads. Instead of relying solely on axial interference (one dimension), the tapered design creates interference in the radial dimension as well, adding a second dimension of interference that fundamentally changes the stress distribution and prevents disengagement under fatigue loading.
2Stability of the object's composition
If high axial interference is introduced to prevent disengagement, then connection stability is improved, but axial tension in pin increases causing fatigue failure
Solution Approach 1:
The patent changes the interference mechanism from purely axial to a combination of radial (diametrical) and axial interference. The tapered thread design introduces radial interference through the taper angle, which prevents disengagement and improves stability without requiring excessive axial interference, thereby protecting the pin from fatigue failure.
Solution Approach 2:
The patent adds radial interference as a second dimension to the connection stability mechanism. Instead of relying solely on axial interference (one-dimensional), the tapered threads create radial interference (second dimension) that actively prevents disengagement, reducing the need for high axial interference and protecting the pin from excessive tensile stresses.
3Reliability
If tapered threaded connection with diametrical interference is used, then fatigue resistance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The patent changes the thread geometry to tapered form with standardized taper ratios (1:16 or 1:20). These standardized parameters allow for controlled manufacturing processes and defined tolerance zones, making it feasible to achieve the required diametrical interference while maintaining practical manufacturing precision levels.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution significantly reduces axial interference, minimizing plastic deformations and stress concentrations, thereby improving the fatigue life and assembly/disassembly performance of sucker rod connections.
Implementation Method 1
This diametrical interference is achieved because the trapezoidal solid shape of one thread goes into the trapezoidal empty shape of another thread, obtaining a wedge effect.
Data Source
AI summary
A sucker rod connection is disclosed. The sucker rod connection comprises a tapered male member including a plurality of trapezoidal threads, and, a tapered female member also including a plurality of trapezoidal threads, in which the male member is capable of being received in threaded engagement with the female member, wherein the threads of the male member are in flank-to-flank contact, both flanks on each thread, with the threads of the female member, thereby creating diametrical interference between the male and female members preventing disengagement and substantially reducing axial interference between the male and female members.