Threaded Pipe Joint Geometry for Metal-to-Metal Sealing
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Solution Overview
Problem
Pipe joints in the oil and gas industry face challenges in maintaining a fluid-tight seal under harsh conditions, including axial compression and tensile forces, pressure differentials, and corrosive fluids, while also needing to withstand repeated assembly and disassembly for reuse without losing performance.
Innovation Solution
A screw-threaded joint design featuring inclined threads at an acute angle with conical stop shoulders and planar sealing surfaces, along with specific torque shoulder angles and surface lengths, reduces galling and ensures a reliable metal-metal seal without additional seal elements, allowing for efficient torque distribution and resistance to forces and corrosion.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded joints are used in oil and gas pipelines, then the joints can be assembled and disassembled for reuse, but they fail to maintain fluid-tight sealing under harsh conditions including axial compression, tensile forces, and pressure differentials
Solution Approach 1:
The patent employs conical surfaces with specific angles (29.5°-30.5°) instead of traditional cylindrical or flat sealing surfaces. The conical geometry provides mechanical advantage under compression while maintaining sealing contact, resolving the contradiction between sealing reliability and repeated assembly by distributing loads more effectively across the sealing interface.
Solution Approach 2:
The patent specifies precise angular parameters (29.5°-30.5°) for the conical sealing surfaces and thread geometry to optimize both sealing performance and assembly characteristics. By carefully controlling these geometric parameters, the joint achieves reliable sealing under pressure while maintaining ease of repeated assembly and disassembly without galling or deformation.
2Device complexity
If traditional threaded connections are employed, then the joint structure is simple, but they suffer from galling, erosion, and corrosion under harsh operating conditions
Solution Approach 1:
The patent applies specific geometric features (conical surfaces with 29.5°-30.5° angles, planar sealing surfaces) to critical local regions where sealing and load transmission occur. This localized optimization of geometry provides enhanced resistance to galling and erosion without significantly increasing overall joint complexity, as the improved surfaces are confined to specific functional zones rather than the entire joint structure.
Solution Approach 2:
The patent combines different surface geometries (conical and planar surfaces) in a composite sealing structure that leverages the advantages of each shape. The conical surfaces provide mechanical strength and load distribution, while the planar surfaces ensure reliable sealing contact, creating a composite joint structure that resists multiple harmful factors simultaneously without requiring additional protective materials or coatings.
3Reliability
If additional seal elements are added to improve sealing, then fluid-tightness is enhanced, but the device complexity and potential failure points increase
Solution Approach 1:
The patent extracts the sealing function from separate seal elements (such as O-rings or gaskets) and integrates it directly into the metal-to-metal contact surfaces of the threaded joint. By incorporating conical and planar sealing surfaces as inherent features of the joint geometry rather than as separate components, the design achieves reliable sealing while reducing device complexity and eliminating potential failure points associated with additional seal elements.
Solution Approach 2:
The patent merges the sealing function with the structural threaded connection by designing the joint geometry itself to provide both mechanical strength and sealing capability. The conical surfaces (29.5°-30.5°) and planar sealing surfaces are integrated into the thread structure, combining load-bearing and sealing functions in a single unified component rather than requiring separate seal elements, thereby reducing complexity while maintaining or enhancing sealing performance.
Data Source
AI summary
A screw-threaded joint for pipes is disclosed comprising a first pipe length having a pin screw threaded portion at one end and a second pipe length having a box portion at one end, the ends each having a screw thread complementary to that on the other pipe length, the threads being adapted to inter-engage along the greater part of the axial length thereof, the threads being inclined in the same direction and at an acute angle to the central longitudinal axis of the joint, the pin thread extending at least to a stop shoulder having a head portion having a substantially conical cross-section which is positioned adjacent a complementary stop shoulder on the box portion.