Steel Pipe Threaded Joint Seal Under Bending Loads
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Solution Overview
Problem
Existing threaded joints for steel pipes face challenges in maintaining sealability under bending loads, as the externally threaded portion and load flank face become displaced, leading to potential thread disengagement and loss of sealability, with no established parameters for load flank angle, torque shoulder angles, and nose shape to ensure sufficient sealability under such conditions.
Innovation Solution
A threaded joint design featuring a negative load flank angle, negative torque shoulder angle, and specific combinations of nose length and pipe outside diameter, with a strain of the seal portion in the circumferential direction of at least 0.30%, and torque shoulder angles smaller than -15°, to enhance sealability and resistance to bending loads.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the externally threaded portion and load flank face are designed with conventional angles, then the threaded joint can be easily manufactured and assembled, but the sealability is lost under bending loads due to displacement and thread disengagement
Solution Approach 1:
The patent applies parameter changes by specifying a negative load flank angle (α) for the threaded portion and a negative torque shoulder angle (β) for the shoulder portion. These angular parameters are changed from conventional positive values to negative values, which fundamentally alters the geometry of the threaded joint to prevent displacement under bending loads while maintaining sealability through the metal-to-metal contact at the seal portion.
2Strength
If the nose length is increased to improve resistance to compression and external pressure, then the structural strength is enhanced, but the overall device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent applies parameter changes by defining the nose length (L) as a specific ratio relative to the pipe outside diameter (d0), where L/d0 ≥ 0.08. This dimensional parameter is optimized to provide sufficient structural strength for resistance to compression and external pressure while maintaining manufacturability through a standardized ratio rather than absolute dimension specifications.
3Stress or pressure
If the seal portion is positioned at the end of the pin nose, then the external pressure resistance is improved, but the resistance to axial compression is reduced due to thinning of the pin nose
Solution Approach 1:
The patent applies dimensional changes by repositioning the seal portion from the end of the pin nose to a location near the threaded portion of the pin nose. This spatial repositioning in the axial dimension allows the pin nose to maintain sufficient thickness for axial compression resistance while the seal portion remains effective against external pressure through its new position where metal-to-metal contact occurs closer to the threaded section.
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 proposed design achieves high sealability and resistance to bending loads, preventing thread disengagement and maintaining fit between pipes, even under increased bending conditions, while minimizing deformation and galling risks.
Implementation Method 1
the outer peripheral face of the nose of the pin and the inner peripheral face of the nose of the box come into metal-to-metal contact with each other at a contact portion, the contact portion serving as a seal portion
Data Source
Figure 1A~1C
Figure 2~3
Figure 4A~4C
AI summary
Provided is a threaded joint for steel pipes having high sealability even under a bending load. To be specific, in the threaded joint, when a pin 3 and a box 1 are threadedly connected with each other, the outer peripheral face of a nose 8 of the pin and the inner peripheral face of a nose of the box are in metal-to-metal contact with each other at a contact portion and the contact portion serves as a seal portion 20. A threaded portion (at which the externally threaded portion 7 and the internally threaded portion 5 are threadedly connected with each other) has a negative load flank angle α, shoulder portions 12 and 14 have a negative torque shoulder angle β, and the ratio L/d0 of a length L of the nose and a pipe outside diameter do is equal to or higher than 0.08.