Steel Pipe Threaded Connection Geometry for High-Pressure Sealing
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Solution Overview
Problem
Existing threaded connections for steel pipes in deep wells with high pressure and temperature environments do not achieve optimal sealing performance, as they are prone to deformation under external pressure, reducing the seal interference and compromising both internal and external pressure sealing.
Innovation Solution
A threaded connection design for steel pipes with a pin and box configuration, where the pin includes a nose, pin shoulder surface, male thread, and pin sealing surface, and the box has a box shoulder surface, female thread, and box sealing surface, with a specific distance ratio (x/L) between the seal position and the end of the male thread optimized between 0.4 and 0.55 to maintain seal interference and stiffness, ensuring improved sealing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pin sealing surface is made with larger diameter to improve sealing performance, then the contact pressure on sealing surfaces increases, but the pin becomes more prone to deformation under external pressure, reducing the real amount of seal interference
Solution Approach 1:
The pin is divided into distinct functional zones: a nose portion at the tip, a pin sealing surface, and a male thread portion. This segmentation allows each zone to perform its specific function - the nose provides structural support and resists external pressure, while the pin sealing surface maintains sealing interference, resolving the contradiction between sealing performance and deformation resistance
Solution Approach 2:
The nose portion is designed with specific geometric characteristics (radius R1, length L1) that differ from the pin sealing surface. This local quality differentiation concentrates the external pressure resistance function in the nose while preserving the sealing function in the pin sealing surface, allowing the pin to maintain both high sealing performance and resistance to deformation
2Reliability
If the amount of seal interference is increased to improve sealing performance, then the contact pressure on sealing surfaces increases, but the complexity of the connection design increases
Solution Approach 1:
The invention optimizes specific geometric parameters of the nose portion (radius R1 between 0.5-2.0mm, length L1 between 5-15mm, and the ratio L1/L between 0.4-0.55) to achieve the desired balance between sealing performance and deformation resistance. By carefully controlling these parameters, the design achieves high reliability without excessive complexity
3Strength
If the nose length is increased to improve stiffness and prevent pin deformation, then the sealing performance against external pressure improves, but the distance between the seal position and the end of the male thread increases, reducing the real amount of seal interference
Solution Approach 1:
The invention establishes an optimal range for the ratio of nose length to pin lip length (L1/L between 0.4-0.55) and specific dimensional parameters (R1 between 0.5-2.0mm, L1 between 5-15mm). This parameter optimization ensures that the nose is long enough to provide sufficient stiffness and resist external pressure, while maintaining the pin sealing surface at an appropriate distance to preserve seal interference and sealing reliability
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 optimized threaded connection maintains high external-pressure sealing performance while maintaining good internal-pressure sealing, preventing seal deformation and ensuring effective sealing across a range of pressures, as validated by finite element analysis.
Implementation Method 1
Each of the sealing surfaces tries to deform to their original diameters and thus produces an elastic recovery force, which causes the sealing surfaces to tightly contact with each other along the entire circumference, thereby providing sealing performance
Implementation Method 2
When the threaded connection is made up, the sealing surfaces has an interference fit, causing the diameter of the pin sealing surface to decrease and the diameter of the box sealing surface to increase
Data Source
AI summary
A threaded connection for steel pipes having improved sealing performance is provided. A threaded connection (10) for steel pipes includes a pin (10) and a box (20). The pin (10) includes a nose (11), a pin shoulder surface (12), a pin sealing surface (13) and a male thread (14). The box (20) includes a box shoulder surface (22), a box sealing surface (23) and a female thread (24). When the position of the portion of the pin sealing surface (13) that first contacts the inner periphery of the box (20) during make-up defines a seal position (P), the distance between the seal position (P) and the end of the male thread (14) adjacent to the pin sealing surface (13) as measured in the pipe-axis direction is denoted by x, and the distance between the tip of the pin (10) and the end of the male thread (14) adjacent to the pin sealing surface (13) as measured in the pipe-axis direction is denoted by L, then, x/L is not smaller than 0.4 and not larger than 0.55.