Mismatched Flanks in Wedge Thread Connections
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Solution Overview
Problem
Wedge thread connections in oilfield tubulars face challenges with indeterminate make-up, high stress during torque application, and trapped pipe dope leading to false torque readings and potential damage due to the close-fitting nature of wedge threads.
Innovation Solution
The introduction of mismatched flanks in wedge thread connections, where at least one of the load or stab flanks has a different angle or profile, creating gaps that allow trapped pipe dope to be relieved and distributed, reducing stress and improving make-up control.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If wedge threads with close-fitting flanks are used to achieve thread seal, then sealing capability is improved, but pipe dope becomes trapped causing false torque readings and potential damage
Solution Approach 1:
The flank surface is segmented into two distinct zones: a first zone with a first flank angle and a second zone with a second flank angle. This segmentation allows the pipe dope to be distributed differently across the zones, with the second zone having greater clearance to prevent trapping while the first zone maintains sealing capability.
Solution Approach 2:
Different portions of the flank surface are given different geometric properties. The first zone has a steeper flank angle optimized for sealing, while the second zone has a shallower flank angle optimized for pipe dope distribution and clearance. This local differentiation resolves the contradiction between sealing and preventing trapped dope.
2Reliability
If wedge threads with close-fitting flanks are used to achieve thread seal, then sealing capability is improved, but stress during torque application increases
Solution Approach 1:
The flank is divided into zones with different angles, allowing stress distribution optimization. The second zone with shallower angle reduces stress concentration during torque application while the first zone maintains sealing integrity.
Solution Approach 2:
The flank angle parameter is varied along the length of the thread engagement. By changing the flank angle from the first zone to the second zone, the stress distribution during torque application is optimized, reducing peak stresses while maintaining sealing.
3Reliability
If wedge threads with close-fitting flanks are used, then make-up control becomes difficult (indeterminate), but thread seal is achieved
Solution Approach 1:
The segmented flank design provides different engagement characteristics in different zones, improving the determinacy of make-up. The transition between zones provides tactile feedback and controlled engagement progression.
Solution Approach 2:
Different zones of the flank provide different functional qualities during make-up. The first zone provides initial engagement and sealing, while the second zone provides controlled progression and determinacy, improving overall make-up control.
Data Source
AI summary
Threaded connections including a pin member and a box member and are mismatched. The pin member and the box member have wedge threads formed thereon with a gap formed between pin and box load flanks and/or pin and box stab flanks of the threaded connection. The mismatch may comprise different flank angles and/or different flank profiles between corresponding flanks.