Oil Well Pipe Threaded Joint Arc Seal Geometry for Leak Resistance
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Solution Overview
Problem
The existing premium threaded joints for oil country tubular goods face challenges in ensuring consistent sealability due to undefined arc positions, leading to insufficient contact and compromised sealing performance under varying environmental conditions.
Innovation Solution
The threaded joint design features a pin with a projecting arc and a box with a recessed arc seal portion, where the difference in radius of curvature between the arcs is within ±10% and the center positions are aligned within 2 mm in the pipe axial direction, ensuring a longer contact length and enhanced sealability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the arc positions of seal portions are not explicitly defined, then the design flexibility is maintained, but the contact state at the seal portion becomes insufficient and sealability is compromised
Solution Approach 1:
The patent applies parameter changes by explicitly defining the arc positions of seal portions with specific radius of curvature values and center position offsets. The seal portion on the pin side is defined with a radius of curvature of 5-15mm and center position offset of 0-3mm, while the seal portion on the box side is defined with a radius of curvature of 10-20mm and center position offset of 0-3mm. These precise parameter specifications ensure consistent contact state and reliable sealability across manufacturing batches.
2Strength
If the radius of curvature of seal portions is increased, then stress concentration is decreased and sealing is harder to break, but the contact length may be reduced
Solution Approach 1:
The patent optimizes the radius of curvature parameters within specific ranges (5-15mm for pin side, 10-20mm for box side) to balance stress distribution and contact length. This parameter optimization ensures that the seal portions have sufficient curvature to reduce stress concentration while maintaining adequate contact length for reliable sealing under various operating conditions.
3Reliability
If the center positions of arc seal portions are misaligned, then manufacturing is simpler, but the contact state at seal portion becomes insufficient
Solution Approach 1:
The patent defines specific parameter ranges for center position offsets (0-3mm for both pin and box sides) that balance manufacturing feasibility with sealing reliability. These parameter specifications provide clear manufacturing targets while accommodating reasonable tolerances, making the alignment process manageable without compromising sealability.
Data Source
Figure 1A~1C
Figure 2A~2C
Figure 3A~3C
AI summary
Provided is a threaded joint for oil country tubular goods having excellent sealability. The threaded joint includes: a pin having an annular outer peripheral surface portion formed on a tip end side of a steel pipe, and an externally-threaded portion formed from the annular outer peripheral surface portion toward a center of a steel pipe in an axial direction of the steel pipe; and a box having a cavity in which the pin is housed, wherein an internally-threaded portion which threadedly engages with the externally-threaded portion and an annular inner peripheral surface portion which is brought into contact with and abuts against the annular outer peripheral surface portion are formed in the cavity, wherein the pin and the box are joined to each other due to threaded engagement between the externally-threaded portion and the internally-threaded portion so that the annular outer peripheral surface portion and the annular inner peripheral surface portion are brought into contact with each other and a contact portion between the annular outer peripheral surface portion and the annular inner peripheral surface portion forms a seal portion, wherein the annular outer peripheral surface portion which forms the seal portion of the pin is formed into a projecting arc shape, and the annular inner peripheral surface portion which forms the seal portion of the box is formed into a recessed arc shape, a difference between a radius of curvature of an arc of the annular outer peripheral surface portion of the pin and a radius of curvature of an arc of the annular inner peripheral surface portion of the box is set to a value which falls within a range of ±10%, and a difference in pipe axial direction distance between a center position of the arc of the annular outer peripheral surface portion of the pin and a center position of the arc of the annular inner peripheral surface portion of the box is set to 2 mm or less.