Asymmetric Threaded Joint for Steel Pipes
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Solution Overview
Problem
Existing threaded joints for steel pipes face challenges in easily inserting pins at a sloping angle and maintaining resistance to compression and galling, especially in severe environments such as deep or horizontal wells, due to the need for chamfers on both pin and box threads which increases costs and reduces stability.
Innovation Solution
A threaded joint design where only one of the pin or box has a two-step stabbing shape with a chamfered portion and a non-chamfered portion, optimizing the chamfer angle and cross-sectional area ratio to facilitate easy insertion while maintaining resistance to compression and preventing galling.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If chamfers are provided on both pin and box threads to facilitate easy insertion at sloping angles, then ease of operation is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The invention extracts the chamfer feature from both pin and box threads and applies it only to the box thread, removing the unnecessary complexity from the pin thread while retaining the insertion facilitation benefit. This selective application reduces overall device complexity and manufacturing cost.
Solution Approach 2:
The invention creates an asymmetric thread structure where the box thread has a two-step profile with chamfered and non-chamfered portions, while the pin thread maintains a standard profile. This asymmetry optimizes the system by applying complexity only where needed for insertion facilitation.
2Ease of operation
If chamfers are provided on both pin and box threads to facilitate easy insertion, then ease of operation is improved, but manufacturing cost increases
Solution Approach 1:
The invention removes the chamfer requirement from the pin thread manufacturing process while maintaining it on the box thread, thereby reducing manufacturing steps and costs without compromising insertion ease.
Solution Approach 2:
Instead of applying chamfers to both components (excessive action), the invention applies the chamfer feature partially only to the box thread, achieving sufficient insertion facilitation while reducing manufacturing cost.
3Reliability
If a two-step stabbing shape with optimized chamfer area ratio is used, then galling resistance is improved, but manufacturing precision requirements increase
Solution Approach 1:
The invention defines specific parameter ranges for the chamfer cross-sectional area ratio (0.25-0.50) and chamfer angle (20-60 degrees) to optimize galling resistance while establishing clear manufacturing specifications that balance precision requirements with practical manufacturability.
Data Source
Figure 1(A)~2
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AI summary
A threaded joint for steel pipes constituted by a pin having male threads and a box having female threads is improved with respect to ease of insertion of the pin and galling resistance of the threaded portions. The stabbing flanks of the threads in a complete thread portion of one of the pin and box has a two-step stabbing shape having a chamfer. The two-step stabbing shape has a stabbing flank angle a of 5 - 45° and a chamfer angle ß of 20 - 60°. The ratio h/H of the chamfer height h to the thread height H of the pin is 0.25 - 0.50, or the ratio of the cross-sectional area of the chamfered portion to the overall cross-sectional area of the stabbing flank is made at least a value corresponding to a chamfer height ratio h/H of 0.25 and at most a value corresponding to a chamfer height ratio of 0.50.