Two-Step Threaded Connection Grooves to Prevent Shoulder Breaks
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Solution Overview
Problem
In two-step thread constructions for threaded connections in oil wells, intermediate shoulder surfaces are difficult to create and prone to breaks under tensile loads due to limited radial dimensions and high strain concentrations at critical cross sections, which complicates the design and manufacturing process.
Innovation Solution
The design incorporates circumferential grooves on the pin and box with curved surfaces contiguous to the intermediate shoulder surfaces, reducing strain and stress concentration while allowing for easier creation of intermediate shoulder surfaces, enhancing torque resistance and sealability through a tapered thread profile and threadless portions, and using a common cutting-tool tip for improved productivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If intermediate shoulder surfaces are provided in two-step thread construction to improve torque resistance, then torque resistance is enhanced, but the surfaces are difficult to create and prone to breaks under tensile loads due to high strain concentrations
Solution Approach 1:
The patent applies curvature by providing a curved surface in the circumferential groove that is contiguous to the intermediate shoulder surface. This curved surface transitions smoothly from the intermediate shoulder surface, reducing stress concentration and making the intermediate shoulder surface easier to create without breaks. The curved surface radius is specifically designed to be larger than the intermediate shoulder surface width, creating a smooth transition that eliminates sharp corners and stress concentration points.
2Reliability
If intermediate shoulder surfaces are made with larger radial dimensions to reduce strain concentration, then break resistance improves, but the connection size exceeds tight size restrictions for flush-type and semi-flush-type connections
Solution Approach 1:
The patent resolves the size conflict by transitioning from a two-dimensional intermediate shoulder surface to a three-dimensional structure with a circumferential groove containing a curved surface. This adds a radial dimension (groove depth) that provides stress relief and break resistance without increasing the axial or outer dimensional footprint of the connection. The curved surface contours within the groove depth, allowing strain distribution in a new dimension while maintaining compact overall size.
3Productivity
If common cutting-tool tip is used to create both intermediate shoulder surfaces and circumferential grooves, then productivity improves, but manufacturing precision must be maintained for complex geometries
Solution Approach 1:
The patent applies universality by designing the circumferential groove and curved surface geometry to be creatable with the same cutting-tool tip used for intermediate shoulder surfaces. The groove dimensions and curved surface radius are specifically designed to match the capabilities of standard cutting-tool tips, allowing a single tool to perform multiple functions (creating both intermediate shoulder surfaces and circumferential grooves) without sacrificing precision. This multi-functional approach maintains manufacturing precision while significantly improving productivity.
Data Source
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AI summary
In a threaded connection of a two-step thread construction including intermediate shoulder surfaces, a break is prevented near the intermediate critical cross sections upon application of a tensile load and the intermediate shoulder surfaces are easier to create, thus improving productivity. The outer periphery portion of the pin 2 located between the intermediate shoulder surface 24 of the pin 2 and the second male thread 27 is provided with a circumferential groove 25 including a curved surface 25a smoothly contiguous to the intermediate shoulder surface 24, thereby mitigating plastic strains generated near the pin intermediate critical cross section PICCS. The inner periphery portion of the box 3 located between the intermediate shoulder surface 35 of the box 3 and the first female thread 32 is provided with a circumferential groove 34 including a curved surface 34a smoothly contiguous to the intermediate shoulder surface 35, thereby mitigating plastic strains generated near the box intermediate critical cross section BICCS.