Wedge-Thread Steel Pipe Connection With High-Angle Shoulder Sealing
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Solution Overview
Problem
Conventional threaded connections for steel pipes face challenges in achieving optimal sealing performance and torque resistance due to the combination of wedge threads and shoulders, which often result in weak points under combined loads and manufacturing tolerance issues.
Innovation Solution
A threaded connection design incorporating a tubular pin and box with inclined circular shoulder surfaces and wedge threads, where the shoulder angle is 4° or larger, ensuring simultaneous locking and shouldering upon make-up, thereby increasing contact forces and maintaining stiffness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional threaded connections use wedge threads with small shoulder angles (0°-20°) to prevent excessive centrifugal force, then sealing performance is maintained, but torque resistance is reduced due to weak points under combined loads
Solution Approach 1:
The patent changes the shoulder angle parameter from the conventional 0°-20° range to a larger range of 20°-60°, which fundamentally alters the force distribution in the thread connection. This parameter change enables the pin tip to effectively resist external pressure while maintaining sealing performance, resolving the contradiction between torque resistance and sealing reliability
Solution Approach 2:
The patent employs a curved sealing surface on the pin instead of a flat surface, creating a spherical or arc-shaped contact area. This curvature allows for more uniform stress distribution and better contact with the box sealing surface, enhancing both sealing performance and torque resistance simultaneously
2Strength
If the outer diameter of the pin shoulder surface is made smaller than the box shoulder surface to prevent pushing force, then sealing contact is maintained, but the pin tip becomes weaker against diameter-reduction deformation
Solution Approach 1:
The patent reverses the conventional dimensional relationship by making the pin shoulder outer diameter equal to or slightly larger than the box shoulder outer diameter. This parameter reversal, combined with the larger shoulder angle, prevents harmful pushing forces while maintaining effective sealing contact through the curved surface geometry
Solution Approach 2:
The curved sealing surface compensates for the changed diameter relationship, ensuring that the pin and box sealing surfaces maintain proper contact. The arc-shaped surface allows for self-adjustment and uniform pressure distribution, maintaining manufacturing precision despite the reversed diameter relationship
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
The design enhances sealing performance and torque resistance by preventing deformation of seal surfaces and maintaining stiffness, with shoulder angles up to 60° providing improved results compared to conventional connections.
Implementation Method 1
Each of the sealing surfaces tries to return to their original diameter and thus produces an elastic recovery, thereby generating contact pressures on the sealing surfaces
Implementation Method 2
The male thread is a wedge thread... When the connection has been made up, the pin and box shoulder surfaces are in contact with each other, a stabbing flank and a load flank of the male thread are in contact with a stabbing flank and a load flank, respectively, of the female thread
Data Source
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AI summary
A threaded connection for steel pipe with improved sealing performance is provided. A threaded connection (1) includes a pin (10) and a box (20). The pin (10) includes a pin shoulder surface (11), a pin sealing surface (12) and a male thread (13). The box (20) includes a box shoulder surface (21), a box sealing surface (22) and a female thread (23). The male thread (13) and female thread (23) are constituted by wedge threads. When the connection has been made up, the pin shoulder surface (11) is in contact with the box shoulder surface (21), the stabbing flank and load flank of the male thread (13) are in contact with the stabbing flank and load flank, respectively, of the female thread (23), and the pin sealing surface (12) is in contact with the box sealing surface (22). The shoulder angle is 4 ° or larger. The shoulder angle is the angle formed by each of the shoulder surfaces (11,21) with a plane perpendicular to the pipe axis (CL) when the connection is not made up.