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 with a tubular pin and box, featuring a nose, pin shoulder, male thread, and pin sealing surface, where the pin sealing surface is formed by a taper and the nose has a smaller taper angle, and the x/L ratio is optimized between 0.4 and 0.55 to maintain seal interference and stiffness, ensuring improved sealing performance against both internal and external pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the pin sealing surface is made with a larger diameter to improve sealing performance, then the contact pressure increases and sealing improves, but the pin becomes more prone to deformation under external pressure
Solution Approach 1:
The patent applies different taper angles to different portions of the pin sealing surface. The first portion (closer to the box) has a larger taper angle to generate higher contact pressure for sealing, while the second portion (closer to the pipe body) has a smaller taper angle to reduce deformation under external pressure. This local differentiation of geometric properties resolves the contradiction between sealing performance and deformation resistance.
Solution Approach 2:
The patent changes the geometric parameter (taper angle) along the length of the pin sealing surface. By varying the taper angle from the first portion to the second portion, the contact pressure distribution is optimized to achieve both good sealing at the critical interface and reduced deformation in the pin body under external pressure.
2Reliability
If the amount of seal interference is increased to improve sealing performance, then the contact pressure on sealing surfaces increases, but the stiffness of the pin near the sealing surface decreases
Solution Approach 1:
The patent creates local quality variation by assigning different taper angles to different portions of the pin. The first portion has a larger taper angle to ensure adequate seal interference and contact pressure for sealing, while the second portion has a smaller taper angle to maintain pin stiffness and resist deformation under external pressure.
Solution Approach 2:
The patent applies partial interference fit principles by concentrating the seal interference primarily in the first portion of the pin sealing surface where it is most needed for sealing, while the second portion maintains sufficient stiffness with reduced interference characteristics.
3Reliability
If the nose length is increased to improve stiffness and prevent deformation, then the sealing performance against external pressure improves, but the manufacturing complexity increases
Solution Approach 1:
The patent optimizes the nose dimensions by specifying precise geometric parameters (taper angles and length ratios) that balance stiffness requirements with manufacturability. The nose length is set to satisfy specific dimensional relationships with other connection components, achieving adequate stiffness without excessive complexity.
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 x/L ratio and design enhance both external and internal pressure sealing performance, maintaining high stiffness and preventing seal deformation, thus providing superior sealing efficiency in harsh environments.
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
The nose increases the stiffness of portions near the pin sealing surface. Thus, when an external pressure is applied to the threaded connection, the pin sealing surface is prevented from being deformed to reduce its diameter
Data Source
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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.