Thread Form for Tubular Connections with Complex Flank Geometry
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Solution Overview
Problem
Existing thread forms for tubular connections in oil and gas wells lack versatility, efficiency, and cost-effectiveness, particularly in forming secure connections that can be quickly assembled and disassembled, and they do not adequately manage radial and diametrical stresses, which can lead to issues during expansion and operation.
Innovation Solution
A thread form featuring a pin member with external threads having two-faceted load flanks and three-faceted, four-radii stab flanks, allowing for controlled radial interfit and stress distribution, enabling secure connections with easier machining and potential for plastic deformation, suitable for both expandable and non-upset applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If traditional thread forms are used for tubular connections, then the connections can be assembled and disassembled, but the assembly process is slow and the connections lack versatility for different applications
Solution Approach 1:
The thread form is divided into distinct functional zones: a stab flank with positive rake angle for rapid initial engagement, a load flank with negative rake angle for secure load-bearing connection, and a root radius for stress distribution. This segmentation allows each zone to perform its specific function optimally, enabling both fast assembly and versatile application.
Solution Approach 2:
Different regions of the thread profile are given different geometric properties: the stab flank has a positive rake angle optimized for quick engagement, the load flank has a negative rake angle optimized for load bearing, and the root has a specific radius for stress control. This local differentiation of properties enables the single thread form to handle multiple functions efficiently.
2Ease of manufacture
If conventional thread designs are used, then manufacturing is straightforward, but radial and diametrical stresses are not adequately controlled leading to connection issues during expansion
Solution Approach 1:
The thread design incorporates specific geometric parameters: a positive rake angle on the stab flank for easy initial engagement, a negative rake angle on the load flank for stress control, and a optimized root radius. These parameter changes maintain manufacturability while significantly improving stress distribution and connection reliability during expansion operations.
3Productivity
If simple thread profiles are used, then machining is easier and faster, but the connections cannot withstand high axial tension and compression loads
Solution Approach 1:
The stab flank with positive rake angle performs the preliminary action of rapid thread engagement and seating, allowing the more complex load-bearing function to be performed efficiently by the load flank. This preliminary engagement action enables faster overall assembly while maintaining high load capacity through the optimized load flank geometry.
Data Source
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AI summary
A thread form is shown which is used to make a threaded pipe connection capable of being screwed together and subsequently unscrewed. A pin member is provided having external threads with stab flanks and load flanks and flat crests and roots for mating with the mating internal threads of a box member to make up a pipe connection. One of the stab or load flanks is made up of two facets and three radii. The other selected flank is made up of three facets and four radii, giving it irregular features forming a complex geometric profiles. The thread form can be used to form a premium threaded connection which is used with such tubulars as casing and tubing for oil, gas, water and waste disposal wells.