Steel Pipe Wedge Thread Connection With Inclined 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, particularly when combining wedge threads with shoulders, as they often result in weak points under combined loads and require precise manufacture tolerances.
Innovation Solution
A threaded connection design featuring a tubular pin and box with wedge threads and inclined shoulder surfaces, where the shoulder angle is 4° or larger, allowing simultaneous contact between the stabbing flanks, load flanks, and shoulder surfaces upon make-up, enhancing contact forces and torque resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional threaded connections use wedge threads with small shoulder angles (0°-20°), then the connection maintains pin tip stiffness, but the seal contact force is insufficient and sealing performance is compromised
Solution Approach 1:
The invention changes the critical parameter of shoulder angle from the conventional 0°-20° range to a larger range of 20°-70°. This parameter change simultaneously increases seal contact force (improving sealing reliability) while maintaining pin tip stiffness through the specific geometric configuration of the shoulder surface that redirects loads away from the pin tip.
2Reliability
If the shoulder angle is increased to improve seal contact force, then sealing performance improves, but the pin tip becomes weaker and loses stiffness
Solution Approach 1:
The invention applies local quality by creating different functional zones: the shoulder surface (with angle 20°-70°) is optimized for generating seal contact force, while the pin geometry in the tip region is configured to maintain stiffness. The shoulder surface acts as a load redistribution zone that protects the pin tip from excessive stresses while ensuring adequate sealing.
3Ease of manufacture
If conventional connections use small shoulder angles, then manufacturing is simpler, but the contact reactive force has centrifugal component that damages sealing surfaces
Solution Approach 1:
By changing the shoulder angle parameter to 20°-70°, the invention transforms the force distribution characteristics. The larger angle reduces the centrifugal component of contact reactive force that damages sealing surfaces, while the shoulder surface geometry is designed to channel forces beneficially toward the seal contact region.
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
This design increases seal contact forces and torque resistance, providing better sealing performance and maintaining stiffness at the pin tip, even with increased shoulder angles, while avoiding the weaknesses associated with conventional combinations of wedge threads and shoulders.
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, which now adhere to each other along the entire periphery to provide sealing performance
Implementation Method 2
a contact reactive force from the box shoulder surface against the pin shoulder surface has no centripetal component and thus does not contribute to the diameter-reduction deformation of the tip of the pin, or has a centrifugal component and resists the diameter-reduction deformation of the tip of the pin
Data Source
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.