Self-Locking Tubular Connection With Variable Thread Widths
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Solution Overview
Problem
Conventional self-locking threaded connections in hydrocarbon well tubing face issues with high shear stresses leading to thread damage under alternating tension/compression, and modifications to increase thread width or number compromise self-locking and torque capacity.
Innovation Solution
A threaded connection design with a male and female end, where the width of the male threads increases and female threads decrease in a controlled ratio, maintaining the total length and wedge ratio, while introducing a constant root width and varying lead profiles to reduce shear stress and maintain torque.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the width of male threads is increased to reduce shear stress, then the resistance to shear stresses is improved, but the lead must be increased which reduces the number of threads and increases the risk of jump-out
Solution Approach 1:
The patent applies local quality by differentiating the thread geometry at different locations along the threaded zone. The male threads have variable width where the first portion (closer to the male end) has a larger width to reduce shear stress, while the second portion (closer to the connection end) has a smaller width. This local differentiation allows the connection to have both high shear resistance at critical locations and sufficient thread engagement length elsewhere to prevent jump-out.
2Reliability
If the number of threads is increased to reduce jump-out risk, then the reliability is improved, but the contact surface area is reduced which decreases the admissible torque
Solution Approach 1:
The patent resolves this contradiction by applying local quality to the thread geometry. By having male threads with variable width (larger at the first portion, smaller at the second portion) and corresponding female threads with complementary variable width, the design concentrates the contact surface area in regions where high torque transmission is needed, while maintaining sufficient thread count overall to prevent jump-out.
3Ease of operation
If conventional self-locking threading is used to take make-up torque through flank contact, then the ease of operation is improved, but the male and female threads are subjected to very high shear stresses causing thread damage
Solution Approach 1:
The patent maintains the self-locking mechanism through flank contact (preserving ease of operation) while applying local quality to the thread geometry. The variable width design of male and female threads ensures that regions subjected to highest shear stresses have optimized dimensions - the first portion of male threads has larger width for shear resistance, while the self-locking flanks maintain contact for easy make-up operation.
Solution Approach 2:
The patent changes the geometric parameters of the threads by implementing variable width along the threaded zone. The male threads transition from larger width at the first portion to smaller width at the second portion, while female threads have complementary variable width. This parameter change allows the connection to accommodate high shear stresses in critical regions while maintaining the self-locking mechanism.
Data Source
AI summary
A threaded connection includes first and second tubular components, each including a respective male and female end. The male and female ends each include at least one threaded zone and finish in a terminal surface. The male threaded zone includes a first portion in which a width of teeth, CWTp, increases from a value CWTpmin corresponding to a width of a tooth closest to the terminal surface of the male end to a value CWTpmax corresponding to a width of a tooth furthest from the terminal surface. A width of teeth CWTb of the female threaded zone decreases from a value CWTbmax corresponding to a width of a tooth furthest from the terminal surface of the female end to a value CWTbmin corresponding to a width of a tooth closest to the terminal surface. The threaded zones cooperate in accordance with a self-locking make-up, with CWTpmin/CWTbmax≥0.2 and CWTbmin/CWTpmax≤CWTpmin/CWTbmax.