Oil Well Threaded Coupling Recess for High-Pressure Sealing
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Solution Overview
Problem
Slim-type threaded connections for oil wells with large wall thickness face challenges in maintaining high sealing performance due to deformation under internal pressure, as conventional designs struggle to prevent diameter increase and resulting leaks.
Innovation Solution
The threaded connection incorporates a tubular coupling with a recess portion of increased wall thickness and length, which provides sufficient stiffness to prevent box deformation, maintaining contact force and sealing performance without increasing the outer diameter of the coupling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If the wall thickness of the box is reduced to achieve slim-type connection with outer diameter equal to pipe body outer diameter, then the outer diameter dimension is reduced, but the box deforms under internal pressure causing diameter increase and seal failure
Solution Approach 1:
The coupling body is segmented into three distinct regions along the axial direction: box regions at both ends and a recess portion in the middle. The recess portion has increased wall thickness compared to the box regions, creating a stiffening structure that prevents overall box deformation while maintaining slim outer diameter dimensions in the connection areas.
Solution Approach 2:
The wall thickness is not uniform throughout the coupling body but is locally optimized. The recess portion has greater wall thickness to provide stiffness and prevent deformation, while the box regions maintain reduced wall thickness to achieve slim overall dimensions. This local quality differentiation resolves the contradiction between size reduction and deformation resistance.
2Productivity
If the wall thickness of the pin and/or box is reduced to achieve connection efficiency smaller than 1, then the connection efficiency is improved, but the sealing performance deteriorates due to box deformation under pressure
Solution Approach 1:
The coupling is segmented such that the recess portion acts as a stiffening element while the box regions maintain efficient but thinner walls. This segmentation allows the connection to achieve high connection efficiency through reduced wall thickness in critical areas while the recess portion prevents catastrophic deformation that would compromise sealing.
Solution Approach 2:
Different wall thicknesses are applied to different functional regions: thinner walls in box regions for efficiency and slim dimensions, thicker walls in the recess portion for structural integrity and deformation prevention under pressure, thereby maintaining both connection efficiency and sealing performance.
3Device complexity
If conventional thread or seal shapes are used in slim-type connections, then the design is simple, but the box deforms under repeated internal pressure causing diameter increase and contact force decrease
Solution Approach 1:
The coupling body is divided into functionally distinct regions with different wall thicknesses. The recess portion with increased wall thickness serves as a pressure-resistant stiffening structure that prevents box deformation under repeated internal pressure, while maintaining the overall slim profile and conventional thread/seal designs in the connection regions.
Solution Approach 2:
The structural properties are locally optimized by providing increased wall thickness only in the recess portion where stiffness is needed to prevent deformation, while other regions maintain conventional designs. This localized reinforcement resolves the contradiction between simplicity and pressure resistance.
Data Source
AI summary
High sealing performance is provided in a threaded connection used for pipes for oil wells with large wall thickness and with a connection efficiency smaller than 1. A threaded connection (10) connects pipes for oil wells (1). The threaded connection (10) includes two pins (11) and a tubular coupling. Each of the pins (11) is provided on an end of the pipe for oil wells (1) and is in continuity with the pipe body (12), which has a wall thickness not smaller than 12 mm. The coupling (2) includes two boxes (21) and a recess portion (22). The box (21) is provided on both ends of the coupling (2). The recess portion (22) has a length not smaller than 10 mm. The threaded connection (10) has a connection efficiency smaller than 1. When the wall thickness of the pipe body (12) is expressed as tpipe, the wall thickness and length of the recess portion (22) are expressed as t1 and 2×L1, respectively, and the length of each of the boxes (21) is expressed as L2, and if the following expressions (1) and (2) define T and L, then, T and L satisfy the following expression (3):T=t1tpipe(1)L=L1L1+L2(2)T·L1/15>1.4(3)