Heavy-Wall OCTG Threaded Joint Geometry for Sealing Without Galling
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Solution Overview
Problem
Conventional threaded joints for heavy-walled oil country tubular goods fail to ensure both sealability and prevent galling under high external pressure and compressive force conditions, as they primarily focus on high compressive force performance without considering external pressure.
Innovation Solution
A threaded joint design featuring a pin with a convex curved nose surface and a tapered box surface, where the seal thickness is set to 15 mm or less, and the shape parameter ts/D is 0.045 or more, along with a complete thread length ratio L/t of 4.0 or less, to achieve balanced sealability and galling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the seal thickness is increased to maintain sealability under high external pressure, then sealability is improved, but the risk of galling increases due to excessive contact pressure
Solution Approach 1:
The patent applies parameter changes by precisely controlling the seal thickness ts to be 15mm or less, and setting the shape parameter ts/D to 0.045 or more. These specific parameter ranges optimize the contact pressure distribution to maintain sealability while preventing excessive pressure that causes galling. The complete thread length ratio L/t is also controlled at 4.0 or less to further regulate stress distribution.
Solution Approach 2:
The patent employs curvature by forming the pin-side seal surface as a convex curved surface and the box-side seal surface as a concave curved surface. This curved geometry distributes the contact pressure more evenly across the seal interface compared to flat surfaces, reducing peak stresses that lead to galling while maintaining effective sealing under external pressure.
2Strength
If the threaded joint is designed for high compressive force resistance, then compression resistance is improved, but sealability under combined high external pressure and compressive force cannot be ensured
Solution Approach 1:
The patent applies local quality by creating distinct functional zones with different geometric characteristics. The seal portion has specific curved surface geometry and controlled thickness for sealing, while the threaded portion has optimized thread geometry for compression resistance. The shoulder portion provides localized stress distribution. Each zone is optimized for its specific function while working together to handle combined loads.
Solution Approach 2:
The patent implements preliminary action through the shoulder design that contacts first during make-up, establishing proper alignment and initial stress distribution before the seal portions engage. The curved seal surfaces are pre-formed to ensure optimal contact geometry is achieved automatically during assembly, preparing the joint for subsequent loading conditions.
Data Source
Figure 1
Figure 2
Figure 3(a)~3(c)
AI summary
Provided is a threaded joint for heavy-walled oil country tubular goods which can acquire both the ensuring of sealability and the prevention of galling in a state where a high external pressure is also applied to the threaded joint in addition to a high compressive force. A surface of a pin 3 side which forms a seal portion 13 and a surface of a box 1 side which forms a seal portion 11 are formed into a convex curved surface and a tapered surface respectively. With respect to the pin 3, a seal thickness ts of the pin is set to 15 mm or less, a shape parameter ts/D (D: outer diameter of a pin raw pipe portion) is set to 0.045 or more, and a complete thread length ratio L/t (L: complete thread length of the pin, t: wall thickness of the pin raw pipe portion) is set to 4.0 or less.