Steel Pipe Threaded Joint Taper Profile for Galling and Fatigue
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Solution Overview
Problem
Existing threaded joints for steel pipes in oil wells face challenges in achieving uniform shot peening on complex thread parts, leading to potential galling and insufficient sealing performance, while also requiring improved anti-fatigue resistance under severe bending loads.
Innovation Solution
A threaded joint design where the taper male thread part is divided into two regions with different taper ratios, with the first region having a greater taper ratio than the second region, which matches or exceeds the taper ratio of the female thread part, enhancing anti-fatigue and galling resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is performed on the thread parts to improve anti-fatigue performance, then the hardness and compressive residual stress are increased, but the surface roughness becomes large which may cause galling
Solution Approach 1:
The patent applies shot peening selectively to specific regions of the thread parts rather than uniformly across all surfaces. By controlling the shot peening application to localized areas where fatigue cracks are most likely to initiate, the patent achieves improved anti-fatigue performance while avoiding excessive surface roughness that would cause galling in other regions.
2Strength
If shot peening is performed uniformly on all thread parts to maximize anti-fatigue performance, then the fatigue strength is improved, but it becomes very difficult to achieve uniform coverage on complex thread shapes and may cause galling in non-specific portions
Solution Approach 1:
The patent divides the thread parts into specific regions that require shot peening and regions that do not. This segmentation approach allows for controlled and uniform application of shot peening to designated areas while avoiding over-treatment of complex geometric features where uniform coverage would be difficult to achieve and could cause galling.
3Strength
If the taper ratio of the male thread part is increased to improve anti-fatigue performance, then the engagement strength is improved, but the sealing performance may be compromised
Solution Approach 1:
The patent optimizes the taper ratio parameter of the male thread part to achieve a balance between engagement strength and sealing performance. By carefully selecting the taper ratio within a specific range, the patent ensures sufficient engagement strength for anti-fatigue performance while maintaining the necessary sealing capability through controlled thread geometry.
Data Source
AI summary
The threaded joint includes a pin and a box. The pin includes a taper male thread part, and the box includes a taper female thread part to be engaged with the taper male thread part. The male thread part is divided into a first region on the free end side of the pin, and a second region on the tubular side of the pin along a tube axis direction. The taper ratio of the first region is greater than the taper ratio of the second region. The taper ratio of the first region is greater than the taper ratio of the female thread part. The taper ratio of the second region is equal to or greater than the taper ratio of the female thread part.