Threaded Connection Double Ellipse Root Profile Fatigue
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Solution Overview
Problem
Existing threaded connections in oil and gas applications, particularly in deep water environments, face challenges with fatigue resistance due to cyclic loading and corrosion, leading to potential ruptures and seal integrity issues.
Innovation Solution
A threaded connection design featuring a double ellipse root profile that maximizes the radius of the stress concentrator, minimizing stress concentration and contact loss, and ensuring maximum contact between load flanks and crests, thereby reducing fatigue stress and galling tendencies.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional thread profiles are used, then manufacturing is simpler, but fatigue resistance deteriorates due to stress concentration at thread roots
Solution Approach 1:
The patent applies curvature by replacing the conventional sharp thread root with a blended root profile that has a continuous curved transition. This eliminates the stress concentration at the thread root by creating a smooth geometric transition between the thread flanks and the root, directly improving fatigue resistance while maintaining manufacturability through standard blending operations.
2Area of stationary object
If flank-to-flank engagement is used, then contact area increases, but contact pressure increases causing galling and seizure
Solution Approach 1:
The patent changes the geometric parameters of the thread profile, specifically the root radius and flank angles, to optimize the distribution of contact pressure. By adjusting these parameters, the contact area is maintained while the peak contact pressure is reduced, preventing galling and seizure during make-up and operation.
3Reliability
If thread root radius is increased to reduce stress concentration, then fatigue resistance improves, but contact area between flanks decreases
Solution Approach 1:
The blended root profile uses a carefully designed curved transition that provides a sufficiently large root radius to reduce stress concentration and improve fatigue resistance, while simultaneously maintaining adequate contact area between mating threads by optimizing the curvature profile to ensure proper flank engagement.
Data Source
Figure 1~1A
Figure 2~2A
Figure 3~3A
AI summary
A threaded connection design having a double ellipse in the thread root for reducing stress fatigue is illustrated in this disclosure. The root groove includes a first portion comprising a first elliptical surface being part of a first ellipse. The root groove further includes a second portion comprising a second elliptical surface, being part of a second ellipse, and the second elliptical surface being joined tangentially at a first end to the first elliptical surface at a junction point that defines the bottom of the root groove. The second elliptical surface is joined tangentially at a second end to the load flank.