Steel Pipe Threaded Connection With Asymmetric Shoulder Sealing
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Solution Overview
Problem
Conventional threaded connections for heavy-wall steel pipes in oil wells face challenges in maintaining sufficient sealing ability against external pressures due to uneven shoulder contact forces and susceptibility to radially-contractive deformation.
Innovation Solution
A threaded connection design featuring a pin and box with inclined shoulder surfaces, where the diameter of the pin's inner circumferential edge is smaller than the box's, resulting in a larger pin seal part thickness and a smaller shoulder contact area, enhancing rigidity and uniformity of the shoulder contact force, thereby stabilizing the seal even under external pressure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If the shoulder surface of the pin and box are designed with equal diameters to maximize contact area, then the shoulder contact area is increased, but the sealing ability against external pressure deteriorates due to uneven contact forces and radial deformation
Solution Approach 1:
The patent applies asymmetry by designing the pin shoulder surface with a smaller diameter than the box shoulder surface. Specifically, the pin shoulder surface has an outer diameter D1 that is smaller than the outer diameter D2 of the box shoulder surface. This asymmetric design creates a stepped configuration where the pin shoulder surface contacts only a portion of the box shoulder surface, concentrating the contact force on a specific annular region. This concentrated contact improves sealing performance against external pressure while maintaining sufficient contact area through the optimized annular contact zone.
2Strength
If heavy-wall steel pipes are used to withstand high external pressures, then the pipe strength is increased, but the sealing ability of the threaded connection deteriorates due to radial contraction deformation
Solution Approach 1:
The patent applies preliminary anti-action by designing the shoulder surface geometry to pre-counteract the radial contraction deformation that occurs when external pressure is applied. The inclined shoulder surfaces are configured with specific angles and dimensions that create a mechanical constraint against radial movement. When external pressure causes radial contraction, the asymmetric shoulder contact geometry generates reaction forces that oppose this deformation, preventing the seal part from separating and maintaining sealing integrity throughout the pressure cycle.
3Ease of manufacture
If the shoulder surfaces are designed to be perpendicular to the pipe axis, then the manufacturing is simplified, but the uniformity of shoulder contact force deteriorates leading to poor sealing
Solution Approach 1:
The patent applies curved surface geometry by designing the shoulder surfaces with inclined angles rather than perpendicular configurations. The pin shoulder surface and box shoulder surface are both inclined at specific angles relative to the pipe axis, creating tapered or conical contact surfaces. This curvature/inclination design ensures that when the pin is threaded into the box, the shoulder surfaces make contact in a manner that distributes force uniformly across the annular contact region, improving sealing consistency while remaining manufacturable through standard machining processes.
Data Source
AI summary
A disclosed threaded connection for steel pipes includes a pin and a box. The pin includes, in order from a front end of the pin toward a pipe body of the pin, an annular shoulder surface, an annular sealing surface located adjacent to the shoulder surface, and a male thread part. The box includes, in order from a pipe body of the box toward a front end of the box, an annular shoulder surface, an annular sealing surface located adjacent to the shoulder surface, and a female thread part. The pin shoulder surface and the box shoulder surface incline from a plane perpendicular to a pipe axis in a direction of screwing the pin. A diameter of an inner circumferential edge of the pin shoulder surface is smaller than a diameter of an inner circumferential edge of the box shoulder surface.