Dual Tapered Threaded Connection for Oil Field Tubulars
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Solution Overview
Problem
Existing gas tight threaded connections for oil and gas wells fail to maintain integrity under high gas pressures and cycling between tension and compression, leading to leaks.
Innovation Solution
A threaded connection design featuring dual helical threads with a straight and tapered portion, where the threads of the pin and box connections are formed from a single continuous helical thread, reducing hoop stress and ensuring a gas-tight seal through a smooth transition and wedging effect, eliminating gaps between thread flanks.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a single helical thread with straight and tapered portions is used, then gas tightness and reliability are improved, but device complexity increases compared to conventional threaded connections
Solution Approach 1:
The single helical thread is segmented into two functional portions: a straight portion for initial engagement and alignment, and a tapered portion for sealing and load bearing. This segmentation allows each portion to optimize its specific function while maintaining a unified thread structure, resolving the contradiction between reliability and complexity.
Solution Approach 2:
Different portions of the thread are given different geometric properties - the straight portion provides uniform engagement for reliable connection establishment, while the tapered portion provides progressive sealing and stress distribution. This local differentiation of thread properties enables gas tightness without requiring entirely complex alternative designs.
2Ease of manufacture
If thread-free sections are used for metal-to-metal seal, then ease of manufacture is improved, but gas tightness deteriorates under high gas pressures and cycling
Solution Approach 1:
The invention converts the potential harm of thread-free sections (which create gaps and leakage paths) into a benefit by using the tapered thread portion to actively wedge and seal against the box connection. The threading action itself becomes the sealing mechanism, transforming the weakness of thread-free sections into a strength through the wedging effect of the tapered geometry.
Solution Approach 2:
The thread geometry transitions from straight to tapered, changing the engagement parameters progressively. This parameter change enables the thread to maintain contact and sealing under varying pressure and loading conditions, preventing gas leakage while remaining manufacturable through standard threading processes.
3Device complexity
If conventional threaded connections are used, then device complexity is reduced, but gas tightness and reliability worsen under high internal pressures and cycling between tension and compression
Solution Approach 1:
The tapered thread portion provides dynamic adaptation to loading conditions. Under tension and compression cycling, the tapered geometry maintains optimal contact and sealing through its self-adjusting wedging action, enabling the connection to reliably withstand high internal pressures and cyclic loading without compromising gas tightness.
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 connection maintains gas tightness and withstands high internal pressures, achieving a 95% compression load test success rate compared to prior art's 60%, demonstrating improved reliability and integrity.
Implementation Method 1
ensuring a gas-tight seal through a smooth transition and wedging effect, eliminating gaps between thread flanks
Implementation Method 2
threads of the pin and box connections are formed from a single continuous helical thread which has a first straight portion and a second tapered portion, reducing hoop stress
Data Source
AI summary
A threaded connection for use on oil field tubular. The connection has a dual tapered thread comprising a dual helical thread having a first, straight threaded portion and a second, angled portion, the threaded connection comprising a pin connection and a box connection both of which have thread-free sections. The thread-free section on the pin and the box are comprised of frustoconical surfaces and cylindrical surfaces. The thread-free section of the pin in addition to having a frustoconical surface and a cylindrical surface has an annular, radially outwardly radiused protrusion which, when the box and the pin connection are made-up is in interference engagement with the frustoconical surface in the box.