Dual-Taper Steel Pipe Thread Connection for External Pressure Sealing
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Solution Overview
Problem
Threaded connections for oil-well pipes in deep wells face challenges in maintaining sealability under high pressure and temperature conditions, where existing designs fail to provide adequate sealability against external pressures while maintaining internal pressure sealability.
Innovation Solution
A threaded connection design for steel pipes featuring a tubular pin and box with specific taper slopes, shoulder surfaces, and sealing surfaces, where the taper slope of the inner male thread is greater than the outer male thread, and the distances between these elements are optimized to enhance sealability against external pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wall thickness of the pin at the sealing portion is increased to improve sealability against external pressure, then the diameter-reduction resistance increases and seal contact force is maintained, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The threaded connection is divided into multiple functional segments: an intermediate portion with optimized wall thickness for external pressure resistance, a first engaged portion for internal pressure sealing, and a second engaged portion for tensile/compressive load bearing. This segmentation allows each portion to be optimized for its specific function without unnecessarily increasing overall complexity
Solution Approach 2:
The pin is designed with non-uniform wall thickness distribution, where the intermediate portion has increased wall thickness specifically at the sealing surface location to resist external pressure, while other portions maintain standard dimensions. This local quality enhancement improves external pressure sealability without globally increasing device complexity
2Reliability
If the taper slope of the inner male thread is increased to improve sealability against external pressure, then the seal contact force increases, but the manufacturing precision requirements increase
Solution Approach 1:
The invention specifies a particular taper slope range for the inner male thread (greater than the outer male thread taper slope) to optimize seal contact force under external pressure. By defining specific parameter ranges rather than exact values, the design achieves reliable sealing while accommodating normal manufacturing variations
3Reliability
If the distance L1 between the tip of the pin and the pin intermediate shoulder surface is increased to improve sealability, then the wall thickness at the intermediate sealing surface increases and diameter reduction resistance improves, but the length of the connection increases
Solution Approach 1:
The invention optimizes the distance L1 as a specific parameter to achieve the desired wall thickness at the intermediate sealing surface while controlling the overall connection length. By carefully selecting L1 within an optimal range, the design balances external pressure resistance with compact dimensions
4Reliability
If the seal interference between pin and box is increased to improve sealability, then the seal contact force increases, but the risk of damage to the sealing surfaces under high tensile/compressive load increases
Solution Approach 1:
The connection is segmented into different functional portions: the intermediate portion with optimized wall thickness handles external pressure sealing, while the first and second engaged portions are designed to bear tensile and compressive loads. This segmentation prevents excessive stress concentration at the sealing surfaces under high loads
Solution Approach 2:
The intermediate shoulder surface is designed with appropriate dimensions and positioning to provide cushioning and stress distribution before loads are transmitted to the sealing surfaces. This beforehand cushioning protects the sealing surfaces from damage under high tensile and compressive loads
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 improves sealability against external pressure by maximizing the wall thickness of the pin at the intermediate sealing surface, reducing diameter reduction under external pressure, and maintaining sufficient seal contact force, while ensuring stability under tensile and compressive loads.
Implementation Method 1
a male thread is screwed into a female thread of the coupling such that they are made up and connected
Implementation Method 2
tensile/compressive loads and external pressures in deep wells are high
Implementation Method 3
both sealing portions tightly contact with each other to achieve an interference fit, forming a seal by metal-to-metal contact
Implementation Method 4
the pin intermediate sealing surface and the box intermediate sealing surface contact each other
Implementation Method 5
it is effective to increase the wall thickness of the sealing portion of the pin, on which the external pressure acts. This increases the diameter-reduction resistance of the sealing portion of the pin upon application of the external pressure
Data Source
Figure 1
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AI summary
A threaded connection for steel pipes is provided that exhibits improved sealability against the external pressure while maintaining the sealability against the internal pressure. A threaded connection for steel pipes includes a pin 10 and a box 20. The pin 10 includes a nose 12, a tapered inner male thread 14, a tapered outer male thread 17, a pin inner sealing surface 13, a pin intermediate shoulder surface 18, a pin intermediate sealing surface 16, and a pin annular portion 15a. The box 20 includes a recess 22 corresponding to the nose 12, a tapered inner female thread 24, a tapered outer female thread 27, a box inner sealing surface 23, a box intermediate shoulder surface 28, a box intermediate sealing surface 26, and a box annular portion 25a. The threaded connection satisfies expressions (1) and (2), provided below. α1 is a taper slope of the inner male thread, and α2 is a taper slope of the outer male thread. α1>α2 and 0.5≦L1α1L2α2≦1.2 In expression (2), L1 is a distance between the tip of the pin and the pin intermediate shoulder surface as measured along the pipe-axis direction when the pin and box have not been made up, and L2 is a distance between the box intermediate shoulder surface and the tip of the box as measured along the pipe-axis direction when the pin and box have not been made up.