Wedge Threaded Steel Pipe Connection for Shear and Torque Resistance
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Solution Overview
Problem
High-torque threaded connections for large-diameter steel pipes experience shear fractures due to insufficient shear strength at the male threadform, leading to concentration of load and subsequent fractures in adjacent threads.
Innovation Solution
The threaded connection design incorporates a male threadform with a first curved surface having a radius of curvature greater than or equal to 0.14 times the thread height, and a thread height between 1.8 mm and 3.0 mm, along with a female threadform with a larger thread height and a clearance to prevent seizure, enhancing shear and torque resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a conventional male threadform with small radius of curvature is used, then the thread can be manufactured with standard cutting depths, but shear fractures occur due to stress concentration at the thread base
Solution Approach 1:
The patent applies curvature by increasing the radius of curvature at the thread base where the load flank meets the thread-groove/root surface. This rounded geometry eliminates stress concentration points that cause shear fractures, while the curvature radius is specifically controlled to be 0.05 times the thread height to balance strength improvement with manufacturing feasibility
Solution Approach 2:
The patent changes the geometric parameters of the threadform by specifying a thread height between 1.8-3.0mm and a radius of curvature of 0.05 times the thread height. These parameter adjustments optimize the balance between shear resistance (improved by larger curvature radius) and manufacturing ease (maintained by controlling absolute dimensions)
2Strength
If the thread height is increased to improve shear resistance, then torque resistance improves, but cutting depth increases making manufacturing more difficult
Solution Approach 1:
The patent optimizes the thread height parameter to a specific range of 1.8-3.0mm. This parameter change ensures sufficient torque resistance while controlling cutting depth to remain manufacturable. The corresponding radius of curvature is set to 0.05 times this optimized thread height to maintain stress distribution
Data Source
AI summary
A high-torque threaded connection with male and female threadforms constituted by wedge threads is provided with high shear resistance and high torque resistance. The radius of curvature r1 of the base of the load flank of the first thread 111, located at the end of the male threadform 11 associated with the tip, is not lower than the thread height Th×0.14, and more preferably not lower than Th×0.16, to improve the shear resistance of the first thread 111. Further, the thread pitch may be reduced to increase the number of threads to increase the area of contact for load flanks, or only the radius of curvature of the base of the load flank of the first thread located at the end of the male threadform associated with the tip may be increased and smaller radii of curvature may be provided for the other portions to increase the area of contact for load flanks, thereby maintaining high torque resistance.