Steel Pipe Thread Profile for Cross-Threading and Compression Loads
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Solution Overview
Problem
Existing threaded connections for steel pipes face challenges in preventing cross-threading and maintaining compression load resistance while ensuring sealing performance, especially in deep oil wells where thermal expansion applies significant tensile and compression loads.
Innovation Solution
The proposed threaded connection features trapezoidal and tapered threads with specific stabbing flank angles and round surfaces, along with controlled interference, to prevent cross-threading and enhance compression load resistance, maintaining effective sealing performance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded connections are used to minimize gaps between steel pipes, then sealing performance against pressure fluid is improved, but the ability to prevent cross-threading and maintain compression load resistance deteriorates
Solution Approach 1:
The patent applies different stabbing flank angles to different portions of the thread structure. The first stabbing flank portion has an angle of -10 to 15 degrees while the second stabbing flank portion has an angle of 20 to 60 degrees. This local variation in geometric properties allows the thread to provide both sealing performance (through the first portion) and cross-threading prevention (through the second portion), resolving the contradiction between these two requirements.
2Reliability
If conventional threaded connections are used to minimize gaps between steel pipes, then sealing performance against pressure fluid is improved, but compression load resistance deteriorates
Solution Approach 1:
The patent employs different stabbing flank angles in different thread portions to simultaneously achieve sealing and compression load resistance. The first stabbing flank portion (-10 to 15 degrees) contributes to sealing performance, while the second stabbing flank portion (20 to 60 degrees) provides enhanced compression load resistance. This local differentiation allows both performance requirements to be met without compromise.
3Ease of operation
If the stabbing flank angle is increased to prevent cross-threading, then cross-threading prevention is improved, but sealing performance deteriorates
Solution Approach 1:
The patent divides the stabbing flank into two distinct portions with different angular characteristics. The first stabbing flank portion has a smaller angle (-10 to 15 degrees) optimized for sealing performance, while the second stabbing flank portion has a larger angle (20 to 60 degrees) optimized for cross-threading prevention. This segmentation allows each portion to perform its specific function without compromising the other, resolving the contradiction between sealing and cross-threading prevention.
4Device complexity
If a single stabbing flank angle is used to simplify manufacturing, then device complexity is reduced, but the ability to simultaneously achieve cross-threading prevention and sealing performance deteriorates
Solution Approach 1:
The patent implements local quality variation by assigning different stabbing flank angles to different portions of the thread. The first portion uses -10 to 15 degrees for sealing, while the second portion uses 20 to 60 degrees for cross-threading prevention and load resistance. Although this increases manufacturing complexity compared to a single angle, it enables simultaneous achievement of multiple performance requirements that would be impossible with a uniform angle.
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 solution effectively prevents cross-threading, maintains compression load resistance, and ensures reliable sealing performance under various pressure conditions, as demonstrated by real-pipe tests and numerical simulations.
Implementation Method 1
The first male thread stabbing flank portion... has a stabbing flank angle of -10 to 15 degrees. The second male thread stabbing flank portion... has a stabbing flank angle of 20 to 60 degrees.
Implementation Method 2
the amount of interference reduces the diameter of the sealing surface of the pin while increasing the diameter of the sealing surface of the box; these sealing surfaces try to return to their respective original diameters, providing an elastic recovery which produces contact pressures on the sealing surfaces
Data Source
AI summary
A threaded connection for steel pipe is provided that prevents cross-threading and provides good compression load resistance. A threaded connection (10) includes a pin (30) and a box (40). The male thread stabbing flank (34) of the pin (30) includes two male thread stabbing flank portions (341) and (342). The male thread stabbing flank portion (341) is located farther from the pipe axis (X) of the steel pipe (20) and has a stabbing flank angle (α1) of −10 to 15 degrees. The male thread stabbing flank portion (342) is located closer to the pipe axis (X) and has a stabbing flank angle (α2) of 20 to 60 degrees. The female thread stabbing flank (44) of the box (40) includes two female thread stabbing flank portions (441) and (442). The female thread stabbing flank portion (441) is located farther from the pipe axis (X) and has a stabbing flank angle (α1) equal to the stabbing flank angle (α1) of the male thread stabbing flank portion (341). The female thread stabbing flank portion (442) is located closer to the pipe axis (X) and has a stabbing flank angle (α2) equal to the stabbing flank angle (α2) of the male thread stabbing flank portion (342).