Well Tubular Thread Form With Elliptical Root for Fatigue Resistance
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Solution Overview
Problem
Current thread forms for well tubulars face challenges in withstanding significant torsional, axial, and thrust loading, particularly in deviated and short radius drilling applications, leading to fatigue issues and reduced torque and tensile capacity, while existing solutions compromise on performance or increase the risk of damage during connection.
Innovation Solution
A novel thread form featuring an elliptical root profile with specific inclinations and radiused transitions, which creates additional mating contact areas and a dope volume, enhancing fatigue resistance, torque, and tensile capacity while maintaining a lightweight design, suitable for both onshore and offshore applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional thread forms are used for well tubulars, then manufacturing is simpler, but fatigue resistance and torque capacity are reduced under significant torsional, axial, and thrust loading
Solution Approach 1:
The patent applies curvature by replacing conventional sharp corners with radiused transitions at critical locations (root and crest). The external thread form includes a root radius R1 and crest radius R2, while the internal thread form includes a root radius R3. These curved transitions eliminate stress concentration points, significantly improving fatigue resistance under torsional and axial loading without adding complex manufacturing steps.
2Force
If thread forms with larger contact areas are designed, then torque and tensile capacity increase, but the risk of damage during connection making increases
Solution Approach 1:
The patent optimizes geometric parameters including flank angles (external load flank 15-25°, external stab flank 5-15°, internal load flank 15-25°, internal stab flank 5-15°), radii (R1, R2, R3), and pitch (6-12 threads per inch). These parameter changes create an optimal balance between contact area for torque capacity and stress distribution to prevent damage during connection making, allowing larger contact areas without increasing damage risk.
3Reliability
If specialized thread profiles are designed for deviated well applications, then resistance to bending and vibration improves, but manufacturing precision requirements increase
Solution Approach 1:
The patent segments the thread form into distinct functional zones: load flanks for torque transmission, stab flanks for engagement, radiused roots for stress relief, and radiused crests for fatigue resistance. This segmentation allows each zone to be optimized independently for its specific function, improving overall reliability under bending and vibration while maintaining manufacturability through standardized geometric features.
Data Source
AI summary
A threaded product is provided having an external thread form on a tubular pin member comprises load and stab flanks on either side of a crest, along with smooth transitions between the crest and flanks. An elliptical root between the flanks aids in reducing stress and forms a dope volume between a non-conforming crest of an internal thread form of a tubular box member. Flanks of the internal thread of the box member contact flanks of the external thread of the pin member to form areas of mating contact on either side of the thread.