Partial Self-Locking Threaded Connection for High-Torque Sealing
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Solution Overview
Problem
Existing self-locking threaded connections for hydrocarbon well applications face limitations in providing high make-up torque and semi-premium sealability while being cost-effective and less prone to damage, especially in applications requiring a maximum outer diameter less than 6% over the nominal diameter, and needing to withstand ISO 13679:2002 CAL-I liquid seal guarantees.
Innovation Solution
A threaded connection design featuring a male and female tubular component with threaded zones having a first portion with increasing thread crest width and a second portion with constant width, allowing only partial self-locking engagement to achieve a semi-premium, semi-flush connection that meets ISO 13679:2002 CAL-I liquid seal standards and API RP 5C:2015 testing protocols, with a simplified assembly process and reduced make-up torque requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If conventional abutment surfaces are used to transmit make-up torque, then the connection can be assembled, but the critical plastication threshold of the abutment surfaces is rapidly reached when too great a make-up torque is applied
Solution Approach 1:
The threaded zone is divided into a locking portion and a non-locking portion. The locking portion engages first to generate initial locking force, while the non-locking portion engages subsequently to provide additional torque transmission capacity without over-stressing the abutment surfaces. This segmentation allows progressive load distribution that prevents rapid reaching of the plastication threshold.
Solution Approach 2:
Different portions of the threaded zone are given different functional qualities: the locking portion has geometry optimized for self-locking engagement with specific flank angles and thread profiles, while the non-locking portion has geometry optimized for torque transmission with different engagement characteristics. This local differentiation allows each portion to perform its specific function optimally without compromising the other.
2Force
If full self-locking threading is used to withstand high torques, then the connection can transmit rotational torque, but the make-up torque requirements and assembly complexity increase
Solution Approach 1:
The threaded zone is segmented into two distinct portions with different engagement characteristics. The locking portion provides the necessary self-locking capability for torque transmission, while the non-locking portion simplifies the overall engagement process. This segmentation reduces the complexity of achieving full self-locking throughout the entire threaded zone while maintaining adequate torque transmission capacity.
Solution Approach 2:
Instead of requiring the entire threaded zone to provide self-locking engagement, only a partial portion (the locking portion) is designed for self-locking. The non-locking portion provides supplementary torque transmission without the complexity of full self-locking geometry throughout, thereby reducing overall device complexity while maintaining sufficient performance.
3Force
If conventional threading with constant thread width is used, then the manufacturing is simpler, but the connection cannot provide both high make-up torque and semi-premium sealability
Solution Approach 1:
The threaded zone employs local quality by varying the thread crest width along the axial direction. The locking portion features increasing thread crest width to optimize self-locking engagement and torque capacity, while the non-locking portion has different dimensional characteristics. This localized variation in geometry provides the necessary performance enhancement for high torque and sealability while maintaining reasonable manufacturability through focused complexity only where required.
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 achieves effective liquid sealing, withstands external pressure, and has a longer lifespan with increased tolerance for machining variations, allowing for cost-effective production and assembly without the need for precise torque charts, while maintaining structural integrity under bending and external pressure.
Implementation Method 1
only a portion of the threaded zone with varying thread width of the male member cooperate by self-locking tightening with a portion of the threaded zone with varying thread width of the female member
Data Source
AI summary
A threaded connection partially in a self-locking arrangement includes a first and a second tubular component provided respectively with male and female threaded zone at their respective ends. Only a portion of a first portion with varying thread width of the male threaded zone cooperates by self-locking tightening with only a portion of the second portion with varying thread width of the female threaded zone when made up one into the other. The connection is able to withstand high torques required for special applications such as drilling with casing or intermediate casing.