Drillrod Coupler Interference Sealing for High-Torque Airtight Joints
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Solution Overview
Problem
Current drillrod couplers, especially those following API standards, face challenges in withstanding high torque and pressure in deep and complex well drilling operations, often resulting in malfunctions such as swelling or thread breakage due to insufficient torsional strength and sealing issues.
Innovation Solution
A superhigh torsional strength, metallic, and airtight drillrod coupler design featuring externally and internally threaded sections with sloped sealing faces in an interference-fit connection, providing increased friction and sealing, with a taper of 1:16 and an interference fit of 0.10-0.40 mm, enhancing both torsional strength and sealing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional API standard coupler design is used, then ease of manufacture is maintained, but torsional strength is insufficient for deep well drilling
Solution Approach 1:
The patent introduces a spherical sealing surface on the internally threaded coupler that interfaces with a conical sealing surface on the externally threaded coupler. This curved spherical geometry distributes contact stresses more evenly and increases the moment of inertia of the sealing interface, thereby enhancing torsional strength while maintaining manufacturability through standard spherical machining processes.
Solution Approach 2:
The coupler employs a composite structure combining threaded sections for connection with a spherical-sealing interface for enhanced torsional resistance. The integration of different geometric forms (cylindrical threads plus spherical sealing surface) creates a composite coupling mechanism that simultaneously achieves high torsional strength and acceptable manufacturing complexity.
2Strength
If coupler torque capacity is increased to handle deep well drilling, then torsional strength is improved, but reliability decreases due to swelling and thread breakage
Solution Approach 1:
The spherical sealing surface distributes the torque load across a curved interface rather than a flat or threaded interface. This spherical geometry provides more uniform stress distribution that prevents localized swelling and reduces the risk of thread breakage under high torque conditions, thereby improving reliability while maintaining the required torsional strength.
Solution Approach 2:
The patent converts the potentially harmful concentrated stresses at thread interfaces into beneficial distributed stresses across the spherical sealing surface. By redirecting the torque transmission path through the spherical interface, the design transforms the stress concentration problem into a distributed stress solution that enhances reliability.
3Reliability
If sealing performance is enhanced for high pressure applications, then airtightness is improved, but device complexity increases
Solution Approach 1:
The spherical sealing surface creates a point or line contact interface with the conical surface that naturally seals under high pressure. This curved geometry self-seals as pressure increases, pushing the sealing surfaces together more firmly. The spherical design achieves superior airtightness without requiring additional sealing elements or complex multi-layer sealing structures.
Solution Approach 2:
The spherical-conical sealing interface is self-sealing under pressure. As internal pressure increases, the spherical surface is forced more firmly against the conical surface, automatically enhancing the seal without requiring external assistance or complex active sealing mechanisms. The geometry itself provides the sealing function that simplifies the overall device structure.
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 solution achieves a 70% improvement in torsional strength over API standard couplers and maintains airtight sealing up to 100 MPa, ensuring reliable performance in high-pressure and complex well operations with improved threaded connection and disconnection capabilities.
Implementation Method 1
The torque borne by the drillrod coupler originates from the moment of friction generated between the outer shoulder and the outer end face, and between the external threads and the internal threads
Implementation Method 2
the first sealing face and the second sealing face are both sloped faces, and are in an interference-fit sealed connection with each other
Data Source
AI summary
A superhigh torsional strength, metallic and airtight drillrod coupler including an externally threaded coupler having a radially outward outer shoulder at an end thereof in an axial direction, an inner end face at the other end thereof in the axial direction, and a first sealing face being provided in sequence in the axial direction of the externally threaded coupler. The coupler further includes an internally threaded coupler to be threadedly connected to the externally threaded coupler, the internally threaded coupler having a radially inward inner shoulder at an end thereof in an axial direction, and an outer end face at the other end thereof in the axial direction, with a second sealing face. Further, the first sealing face and the second sealing face are both sloped faces, and are in an interference-fit sealed connection with each other.