Dual-Taper Steel Pipe Threaded Connection for External Pressure
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Solution Overview
Problem
Existing threaded connections for oil-well pipes face challenges in maintaining sealability against external pressure while ensuring internal pressure sealability, particularly in deep wells with high tensile/compressive loads and external pressures.
Innovation Solution
A threaded connection design for steel pipes featuring a tubular pin and box with specific taper slopes, sealing surfaces, and shoulder surfaces, where the taper slope of the inner male thread is greater than the outer male thread, and the distances and areas of these components are optimized to enhance sealability, ensuring a well-balanced thickness distribution.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the wall thickness of the sealing portion of the pin is increased to improve sealability against external pressure, then the diameter-reduction resistance increases and seal contact force is maintained, but the overall device complexity and manufacturing difficulty increase
Solution Approach 1:
The threaded connection is divided into multiple functional segments: an intermediate sealing portion with optimized wall thickness for external pressure resistance, an inner sealing portion for internal pressure sealing, and distinct thread portions. This segmentation allows each portion to be optimized for its specific function, with the intermediate portion providing external pressure sealability through controlled wall thickness without unnecessarily complicating the entire connection structure.
Solution Approach 2:
Different wall thicknesses are applied to different portions of the pin. The intermediate sealing portion has a specifically optimized wall thickness that balances external pressure resistance with manufacturing feasibility, while other portions have different thicknesses suited to their functions. This local differentiation improves external pressure sealability without requiring uniform increases in complexity throughout the entire connection.
2Reliability
If the taper slope of the inner male thread is increased to improve thread engagement and sealability, then the thread locking force increases, but the manufacturing precision requirements increase
Solution Approach 1:
The patent specifies a particular taper slope range for the inner male thread (greater than the outer male thread taper slope) to optimize both thread engagement and sealability. By defining specific parameter ranges rather than exact values, the design achieves reliable sealing while allowing for normal manufacturing tolerances, thus balancing sealability with manufacturing feasibility.
3Reliability
If the distance L1 (from pin tip to intermediate shoulder surface) is increased to improve external pressure sealability, then the wall thickness at sealing portion increases, but the overall connection length increases
Solution Approach 1:
The patent defines specific relationships between geometric parameters (L1, L2, taper slopes) to optimize external pressure sealability while controlling overall length. By establishing parameter relationships rather than fixed dimensions, the design achieves improved external pressure resistance through optimized wall thickness distribution without necessarily increasing the overall connection length proportionally.
Data Source
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 and a box. The pin includes a nose, a tapered inner male thread, a tapered outer male thread, a pin inner sealing surface, a pin intermediate shoulder surface, a pin intermediate sealing surface, and a pin annular portion. The box includes a recess corresponding to the nose, a tapered inner female thread, a tapered outer female thread, a box inner sealing surface, a box intermediate shoulder surface, a box intermediate sealing surface, and a box annular portion. 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(1)0.5≦L1α1L2α2≦1.2(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.