Stepped Pitch Line Thread Form for Tubular Connections
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Solution Overview
Problem
Existing tubular connections in the Oil & Gas industry face challenges in achieving high compression ratings and resistance to axial compressive loading, particularly in slim-diameter and flush-type connections, where the current thread forms do not effectively distribute stress across a wide area, leading to limited compressive capacity and potential damage under mechanical or thermal loads.
Innovation Solution
The development of a tubular connection with a tapered, constant pitch thread featuring a stepped pitch line, where the stab flank of the pin and box members have distinct surfaces with varying angles, resulting in a wide radial band of substantive contact upon full make-up, enhancing the cross-sectional area to resist compressive loads and improve tri-axial pressure integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If traditional thread forms are used in slim-diameter and flush-type connections, then the connection can be made compact with minimized outer diameter, but the compressive capacity and resistance to axial compressive loading is limited
Solution Approach 1:
The thread form incorporates a stepped pitch line with multiple levels (first pitch line at major diameter, second pitch line at intermediate diameter, third pitch line at minor diameter) that creates different contact zones. This local variation in contact geometry allows the connection to maintain compact outer dimensions while developing compressive strength through progressive engagement of thread surfaces at different radial positions.
Solution Approach 2:
The invention transitions from traditional single-plane thread contact to multi-level stepped contact across different radial dimensions. The stepped pitch line creates a three-dimensional contact pattern that engages thread surfaces at multiple heights, effectively utilizing the radial dimension to increase load-bearing area without increasing the connection's outer diameter.
2Device complexity
If traditional thread forms with single-plane contact are used, then the thread structure is simple, but the stress distribution is concentrated leading to limited compressive strength
Solution Approach 1:
The thread form is segmented into multiple contact levels along the pitch line, creating distinct engagement zones at different radial positions. This segmentation distributes the compressive load across multiple discrete contact points rather than concentrating it at a single plane, thereby increasing overall compressive strength while maintaining a relatively straightforward thread geometry.
Solution Approach 2:
The invention modifies the pitch line parameter from a traditional single continuous line to a stepped configuration with discrete levels at major, intermediate, and minor diameters. This parameter change transforms the stress distribution pattern from concentrated to distributed, enabling the thread structure to achieve higher compressive strength without proportionally increasing complexity.
3Ease of operation
If conventional thread flanks with clearance are used, then the threads can be assembled without damage, but the contact area is limited to point or line contact unable to absorb sufficient stress
Solution Approach 1:
The stepped pitch line configuration is designed to guide the threading operation through progressive engagement. The first pitch line at the major diameter provides initial contact and guidance during assembly, followed by sequential engagement of intermediate and minor diameter pitch lines as threads are made up. This preliminary action sequence ensures damage-free assembly while progressively building comprehensive surface contact for stress absorption.
Solution Approach 2:
The thread form transitions from static point/line contact to dynamic multi-level surface contact during the make-up process. As torque is applied and threads are driven together, the contact pattern evolves from initial engagement at outer diameters to progressive engagement of inner diameters, ultimately achieving widespread surface contact that can dynamically absorb applied stresses.
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
This configuration significantly increases the compressive capacity of the connection by distributing stress across a wider area, limiting movement, and protecting the metal seal during mechanical or thermal cycles, thereby improving the overall performance and integrity of the tubular connection.
Implementation Method 1
The stab flank of the pin member thread interacts with the stab flank of the box member thread during connection make-up to move the load flank of the pin member thread into substantive contact with the load flank of the box member thread
Data Source
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AI summary
A tubular connection is formed by a box member and a pin member, each of which has a tapered constant pitch thread. A profiled defined by the thread of at least one of the pin member and the box member results in a pitch line (44) that is a stepped pitch line. The stepped pitch line configuration may produce a wide radial band of substantive contact between the stab flanks of the pin member and box member upon full make-up of the connection.