Threaded Joint Sealing with Toroidal and Frusto-Conical Surfaces
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Solution Overview
Problem
Existing threaded joints for pipes in ultra-deep oil exploration and high-pressure environments fail to match the performance of thick-walled pipes under extreme conditions, experiencing plastic deformations and galling due to high pressures and temperatures, and are not suitable for pipes with wall thicknesses greater than standard ranges.
Innovation Solution
A threaded joint design featuring dual metal-to-metal seals, with toroidal and frusto-conical surfaces, optimized for thick-walled pipes, providing internal and external sealing efficiency while avoiding galling, and incorporating a hooked thread and specific geometric variables to maintain structural stability and reduce contact pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If standard threaded joints are used for thick-walled pipes under ultra high pressure, then the joint structure is simple and easy to manufacture, but the joint experiences plastic deformations and galling, failing to match pipe body performance
Solution Approach 1:
The joint is segmented into multiple functional zones: a sealing zone with metal-to-metal contacts for pressure sealing, and a load-bearing zone with optimized thread geometry for mechanical strength. This segmentation allows each zone to be optimized independently for its specific function while maintaining overall joint integrity under ultra high pressure
Solution Approach 2:
Different geometric parameters are applied to different parts of the joint: the sealing surfaces have specific toroidal and frusto-conical profiles for pressure distribution, while the thread body has optimized pitch and depth for load bearing. This local differentiation of geometric quality enables the joint to simultaneously achieve sealability and structural capacity matching thick-walled pipe performance
2Reliability
If high interference and torque values are applied to achieve sealability at ultra high pressure, then sealing performance improves, but critical plastic deformations and galling occur during make-up operations
Solution Approach 1:
The joint geometry is pre-designed with specific toroidal and frusto-conical sealing surfaces that create optimal contact pressure distribution from the beginning of the make-up process. This preliminary geometric configuration ensures that sealing is achieved progressively at lower torque values, preventing plastic deformations and galling that would occur with conventional high-torque make-up operations
Solution Approach 2:
Toroidal sealing surfaces with specific radii are employed to distribute contact pressure evenly across the sealing interface. The curved geometry of the toroidal surfaces, combined with frusto-conical profiles, creates a progressive contact pattern during make-up that reduces peak stresses and prevents galling while maintaining sealability at ultra high pressure
3Ease of manufacture
If joints are designed for standard wall thickness pipes, then the design is optimized for standard applications, but the performance becomes unpredictable when applied to pipes with thicker walls under extreme conditions
Solution Approach 1:
The joint design incorporates specific geometric parameters including toroidal surface radii, frusto-conical angles, and thread dimensions that are optimized for thick-walled pipe applications. These parameter changes from standard joint designs enable the joint to maintain predictable performance and match pipe body strength under the extreme pressures and temperatures encountered in ultra-deep well applications
Data Source
AI summary
A threaded joint for joining tubes used especially in the field of OCTG (Oil Country Tubular Goods), such as pipes in gas or oil production and/or casings when drilling wells can include a pin and a coupling, or box, having an end surface not facing against any surface of the pin when the joint is made-up. Following make-up of the joint, first sealing surfaces of the pin and box mate to form an internal metal-to-metal seal, and second sealing surfaces of the pin and box mate to form an external metal-to-metal seal, where the internal and external seals are defined by contact between one toroidal surface and one frusto-conical surface.