Sucker Rod Connection with Tangential Elliptical Thread Roots
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Solution Overview
Problem
Standard sucker rod connections in subterranean pumping systems are prone to fatigue and stress corrosion cracking due to high cyclic stresses and limited root radii, leading to reduced durability and increased risk of failure.
Innovation Solution
The implementation of tangential elliptical root threads in sucker rod connections, optimized with larger pitch, equivalent root radius, and smaller flank angle, along with a stress relief groove, to reduce stress concentration and enhance fatigue strength, and the use of rolling dies and forming taps for thread formation to minimize stress corrosion cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If standard sucker rod connections are used, then the structure is simple and easy to manufacture, but the fatigue strength is low and stress corrosion cracking occurs
Solution Approach 1:
The patent applies parameter changes by modifying the thread root geometry from standard circular or flat roots to elliptical roots with specific dimensional ratios. The elliptical root profile is defined by major and minor axis dimensions that create optimized stress distribution characteristics, transforming the geometric parameters to achieve superior fatigue resistance while maintaining manufacturability through controlled variable changes.
Solution Approach 2:
The patent employs spheroidality by implementing curved elliptical root profiles instead of straight or flat thread roots. The elliptical geometry provides continuous curvature that smoothly transitions stresses along the thread root, eliminating sharp corners and stress concentration points. This curved geometry fundamentally changes the stress flow pattern to prevent fatigue crack initiation.
2Reliability
If standard thread roots with limited radii are used, then the manufacturing is easier, but the stress concentration is high leading to cracking
Solution Approach 1:
The patent changes the geometric parameters of the thread root from standard dimensions to elliptical dimensions with optimized major and minor axis ratios. This parameter transformation creates larger effective root radii that reduce stress concentration factors while remaining compatible with conventional thread rolling and forming processes, thus maintaining ease of manufacture while dramatically improving reliability.
Solution Approach 2:
The patent applies local quality by optimizing the thread root geometry specifically at the critical stress concentration zone without altering other thread parameters. The elliptical root profile is implemented only at the root region where stress concentration occurs, leaving the thread flanks and crest unchanged. This localized geometric optimization targets the specific problem area while maintaining overall thread compatibility and manufacturability.
3Duration of action of stationary object
If high cyclic stresses are endured, then the operational capability is maintained, but fatigue and cracking occur reducing durability
Solution Approach 1:
The patent implements beforehand cushioning by designing the elliptical thread root geometry to preemptively reduce stress concentrations before fatigue cracks can initiate. The optimized elliptical profile acts as a stress-cushioning feature that distributes cyclic loads more evenly, preventing the high peak stresses that would otherwise lead to fatigue failure. This geometric cushioning is built into the connection design to withstand high cyclic stresses throughout the service life.
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
This design significantly increases the fatigue strength of sucker rod connections by up to fivefold and reduces the risk of stress corrosion cracking, ensuring enhanced performance and longevity under harsh operational conditions.
Implementation Method 1
pin threads where the pin threads include tangential elliptical roots formed with rolling dies
Implementation Method 2
coupling threads that include tangential elliptical roots formed with forming taps
Data Source
AI summary
A pump rod can include a body that includes a longitudinal axis; and a pin at an end of the body where the pin includes threads where the threads include tangential elliptical roots.