Steel Pipe Threaded Connection Geometry for Pressure Sealability
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Solution Overview
Problem
Existing threaded connections for steel pipes in oil wells face challenges in maintaining sealability against internal and external pressures, particularly due to thermal expansion and varying diameters, which can lead to reduced contact pressures and inefficiencies in deep well environments.
Innovation Solution
A threaded connection design featuring a pin with a nose and pin sealing surface, and a box with a corresponding sealing surface, where the seal-point distance is 13 mm or higher, and the seal wall-thickness ratio is 1.7 or higher, providing improved sealability by maintaining contact pressure under compressive loads and internal pressures.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the diameter of the sealing surface of the pin is made slightly larger than the diameter of the sealing surface of the box to create interference for metal-to-metal sealing, then sealability is improved, but the contact pressure distribution becomes uneven and seal reliability decreases under thermal expansion and compressive loads
Solution Approach 1:
The patent changes the geometric parameters of the sealing surfaces by introducing a shoulder angle (2-15 degrees) and specific curvature radii (R1=0.5-2.0mm, R2=1.0-3.0mm) to optimize contact pressure distribution. This transforms the sealing mechanism from interference-fit based to geometry-controlled elastic deformation based, maintaining sealability while improving pressure distribution uniformity under various loads
Solution Approach 2:
The patent creates a dynamic sealing mechanism where the curved surfaces and shoulder angle allow the sealing surfaces to adapt their contact pattern under different loading conditions. The elastic deformation of the pin and box materials dynamically adjusts the contact pressure distribution, ensuring reliable sealing whether under internal pressure, external pressure, or thermal expansion conditions
2Productivity
If threaded connections with equal or slightly larger inner and outer diameters are used to minimize gaps between pipes in deep wells, then drilling efficiency is improved, but sealability against internal and external pressures becomes more difficult to maintain
Solution Approach 1:
The patent optimizes the dimensional parameters of the connection components, specifically setting the shoulder angle between 2-15 degrees and the curvature radii R1=0.5-2.0mm and R2=1.0-3.0mm. These parameter changes create an elastic deformation mechanism that maintains seal contact pressure even when the overall pipe diameter is minimized for deep well applications
Solution Approach 2:
The patent segments the sealing function from the structural function by introducing a dedicated sealing structure with curved surfaces and shoulder angles. This allows the connection to simultaneously achieve minimal diameter for drilling efficiency while maintaining reliable sealing through the specialized sealing geometry that creates uniform contact pressure distribution
3Ease of manufacture
If the pin and box are made with standard wall thicknesses to reduce manufacturing complexity, then ease of manufacture is improved, but sealability under high compressive loads and thermal expansion deteriorates
Solution Approach 1:
The patent establishes specific parameter ranges for wall thickness ratios and dimensional proportions that optimize sealing performance under compressive loads and thermal expansion. By defining these parameters as ranges rather than fixed values, the patent maintains ease of manufacture while ensuring reliable sealing through geometric control of elastic deformation behavior
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 design enhances sealability and torque performance by maintaining high contact pressures and resistance to external and internal pressures, ensuring efficient operation in deep well environments.
Implementation Method 1
the interference causes a reduction in the diameter of the sealing surface of the pin and causes an increase in the diameter of the sealing surface of the box, and each of the sealing surfaces tries to recover their original diameters and thus produces elastic recovery forces, which produce contact pressures on the sealing surfaces to cause them to adhere to each other
Implementation Method 2
if oil-well pipes are used in an oil well with great depth, for example, thermal expansion of a pipe may apply large tensile loads or compressive loads to the associated threaded connection
Data Source
AI summary
A threaded connection for steel pipe with improved sealability against the internal and external pressures is provided. A threaded connection 1 includes a pin 10 and a box 20. The pin 10 includes a male thread 11, a nose 12, a pin shoulder surface 13, and a pin sealing surface 14. The box 20 includes a female thread 21, a box shoulder surface 23, and a box sealing surface 24. The box sealing surface 24 has a seal point SP on the taper surface 242 located at the midpoint thereof as determined along the direction of the pipe axis CL. The distance LSP between the tip of the nose 12 and the seal point SP as measured in the direction of pipe axis CL is 13 mm or larger. The shoulder angle α between the pin or box shoulder surface 13 or 23 and a plane VP perpendicular to the pipe axis CL is 2 to 13 degrees. The ratio TB/TP of the wall thickness TB of the box to the wall thickness TP of the pin 10 as measured at the seal point SP is 1.7 or higher.