Rotary Shoulder Drill Pipe Connection for Thread Alignment
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Solution Overview
Problem
Conventional API 5-inch drill pipes suffer from poor hydraulic efficiency, mechanical performance, box swell, pin collapse, and premature fatigue failure due to misalignment of threads under high axial, torsional, and bending loads.
Innovation Solution
The development of a drill pipe with a rotary shoulder connection featuring primary and secondary angled or curved shoulders, which includes specific dimensions and thread forms to enhance alignment and durability, using materials like low alloy steels and stainless steels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If standard tapered threads with high included angle are used in box connections, then thread strength is improved, but box swell occurs due to material yielding under axial compressive loads
Solution Approach 1:
The patent changes the thread geometry parameters by using a square thread form with zero included angle instead of traditional tapered threads with high included angles (e.g., 60 degrees). This parameter change eliminates the wedge action that causes box swell while maintaining thread strength through proper load distribution across the square thread flanks.
Solution Approach 2:
The patent introduces curved shoulders with specific radii (e.g., R0.0625 to R0.125 for primary shoulders, R0.03125 to R0.0625 for secondary shoulders) to replace traditional sharp or flat shoulder transitions. These curved transitions distribute stresses more evenly and eliminate stress concentration points that would otherwise cause box swell under axial compression.
2Device complexity
If standard single-shoulder connections are used, then device complexity is reduced, but premature fatigue failure occurs under high alternating axial, torsional, and bending loads
Solution Approach 1:
The patent divides the connection structure into multiple functional segments: a primary shoulder for axial load bearing and sealing, and a secondary shoulder for additional structural support and alignment. This segmentation allows each shoulder to be optimized for its specific function, improving fatigue resistance under alternating loads while maintaining manageable complexity.
Solution Approach 2:
The patent employs composite construction by combining different geometric features (square threads, curved shoulders, flat surfaces) within the same connection assembly. The primary and secondary shoulders use different radii and orientations to create a composite structural system that resists multiple types of stresses simultaneously, enhancing reliability under complex loading conditions.
3Adaptability or versatility
If conventional API 5-inch drill pipe dimensions are used, then compatibility with existing equipment is improved, but hydraulic efficiency and mechanical performance deteriorate
Solution Approach 1:
The patent applies local quality by modifying only the connection region (tool joint) while maintaining the standard API 5-inch drill pipe body dimensions. The square threads and curved shoulders are localized to the connection area, allowing compatibility with existing drilling equipment while achieving superior hydraulic efficiency through the improved connection geometry that reduces flow restrictions and stress concentrations.
4Ease of manufacture
If standard thread profiles with high included angles are used, then ease of manufacture is improved, but thread misalignment and permanent damage occur under high loads
Solution Approach 1:
The patent uses curved shoulders with precisely controlled radii to guide thread engagement and maintain alignment under load. The curved transition surfaces ensure that square threads engage uniformly along their length, preventing misalignment and permanent damage while remaining manufacturable through standard machining or forming processes.
Data Source
AI summary
A drill pipe comprises a drill pipe body and a tool joint that comprises a rotary shoulder connection is disclosed. The rotary shoulder connection comprises: a box connection, wherein the box connection has a box outer radius, a box counter bore radius and a box inner radius, and box threads having a box thread form cut along a box taper: a pin connection, wherein the pin connection has a pin outer radius, a pin cylinder radius and a pin nose radius, and pin threads having a pin thread form cut along a pin taper to align with the box threads inside the box connection; and a primary shoulder connection comprising: a primary box shoulder that is angled or curved; and a primary pin shoulder that is angled or curved. Methods of using the drill pipe are also disclosed.