Steel Pipe Threaded Joint With Pressure-Amplified Seal Surfaces
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Solution Overview
Problem
Screw joints for steel pipes, particularly those made of high alloy steel with chromium, face a challenge in achieving both high galling-resistant performance and sealing performance, as existing solutions either compromise on sealing due to reduced contact pressure or risk fluid leakage with excessive pressure.
Innovation Solution
The screw joint design incorporates a dovetail-shaped screw and hook shoulders adjacent to the seal surfaces, with tapered and curved surfaces that maintain contact at a wide width during assembly, and a contact pressure amplification mechanism to ensure stable sealing and galling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the seal interference amount is increased to improve sealing performance, then the sealing performance is improved, but galling occurs on the seal surfaces during make-up
Solution Approach 1:
The seal surface is divided into two distinct regions: a first seal region with a larger radius of curvature and a second seal region with a smaller radius of curvature. This segmentation allows different portions of the seal surface to serve different functions - the first region provides a larger contact area to distribute pressure and reduce galling, while the second region maintains adequate contact pressure for sealing performance.
Solution Approach 2:
Different regions of the seal surface are given different geometric properties. The first seal region has a larger radius of curvature creating a more gradual slope, while the second seal region has a smaller radius of curvature creating a steeper slope. This local differentiation optimizes each region for its specific function within the overall sealing system.
2Object-affected harmful factors
If a lubricating coating or surface treatment coating is formed on the seal surface to improve galling-resistant performance, then the galling-resistant performance is improved, but the coating may peel off due to rough handling during transport
Solution Approach 1:
The seal surface geometry itself provides the galling-resistant function through its dual-radius curvature design, eliminating the need for external lubricating coatings or surface treatments. The optimized contact pressure distribution inherent in the geometric design protects against galling without requiring additional protective layers that could peel during handling.
3Reliability
If the seal surfaces contact each other in a narrow range to increase local contact pressure for sealing, then the sealing performance is improved, but galling occurs more easily
Solution Approach 1:
The seal contact area is segmented into two regions with different pressure characteristics. The first seal region provides a larger contact area that distributes the load and reduces peak pressures, while the second seal region concentrates pressure to ensure adequate sealing. This segmentation resolves the contradiction between needing high contact pressure for sealing and avoiding excessive pressure that causes galling.
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
This design effectively reduces the risk of galling and maintains stable sealing performance by optimizing contact pressure distribution, ensuring the screw joint performs well in high alloy steel and other challenging materials.
Implementation Method 1
the pin and the box are fitted and interfere with each other in a radial direction, and thus, elastic restoration forces which try to revert to the original diameters of each of the box and the pin are generated between the box enlarged in diameter and the pin reduced in diameter. The seal surfaces can come into close contact with each other over the entire circumference using the elastic restoration forces.
Data Source
Figure 1~2
Figure 3A~3B
Figure 4A~4C
AI summary
In a screw joint for a steel pipe, a taper angle of a tapered surface of a pin is substantially the same as a taper angle of a tapered surface of a box. In addition, the pin and the box interfere with each other in a radial direction while a seal surface of the pin and a seal surface of the box contact each other in a process of make-up between a male screw portion and a female screw portion, and at least a part of the seal surface of the pin comes into close contact with at least a part of the seal surface of the box over the entire circumference. Moreover, a contact pressure amplification mechanism, which increases a contact pressure between the seal surface of the pin and the seal surface of the box at the completion of the make-up, is further provided.