Expandable Pipe Section Threaded Joint Design
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Solution Overview
Problem
Existing threaded joints in hydrocarbon well casings face issues with maintaining structural integrity and gas tightness during and after expansion, as they are prone to loosening due to radial and axial expansion, and cannot withstand cyclic loads and fatigue without risking unintentional separation.
Innovation Solution
The threaded joints are designed with cylindrical surfaces and a stepped configuration, featuring circular or oval thread roots and crests with a curved transition, and a sealing element made of soft material like silver, which distributes loads and reduces stress concentrations, ensuring the joint remains locked and gas tight during expansion and subsequent operations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional threaded joints are used in expandable pipe sections, then the joint can be assembled and initially secured, but the joint loosens and loses gas tightness during radial and axial expansion
Solution Approach 1:
The thread root and thread crest are designed with circular or oval shapes instead of sharp edges, creating rounded profiles that distribute stress more evenly during expansion. This curvature prevents stress concentration points that would otherwise cause thread loosening and maintains joint integrity under radial and axial loads.
Solution Approach 2:
The threaded connection geometry is modified with specific dimensional parameters including thread pitch, thread angle, and rounded thread profiles. These parameter changes create a threaded joint that can accommodate the dimensional changes during expansion while maintaining secure engagement and gas tightness.
2Volume of moving object
If the pipe is expanded using conventional methods, then the pipe diameter increases to fit the wellbore, but the threaded joint bends and loosens during the expansion process
Solution Approach 1:
The rounded thread root and crest profiles absorb and distribute the bending stresses generated during expansion. The curved geometry allows the threads to flex without creating sharp stress concentrations that would cause joint failure, enabling the pipe to expand while maintaining joint strength.
Solution Approach 2:
The threaded section is designed with specific local geometric properties including rounded profiles and optimized thread dimensions that differ from the rest of the pipe. This local quality enhancement at the joint region provides targeted stress distribution and maintains joint integrity during the global expansion process.
3Ease of operation
If the threaded joint is designed for initial assembly, then the pipe sections can be connected, but the joint cannot withstand cyclic loads and fatigue during subsequent operations
Solution Approach 1:
The rounded thread profiles eliminate sharp corners and stress concentration points that would initiate fatigue cracks under cyclic loading. The smooth curved geometry distributes stresses evenly throughout the thread engagement, allowing the joint to withstand repeated loading cycles including tension, compression, and rotational moments.
Solution Approach 2:
Instead of designing threads with sharp edges for easy manufacturing and then trying to protect them from fatigue, the design inverts the approach by using rounded profiles from the outset. This inversion prioritizes fatigue resistance while maintaining ease of assembly through the smooth, continuous thread geometry.
Data Source
AI summary
An expandable pipe section, intended to be joined with a corresponding pipe section for use in connection with a well casing of a production well for hydrocarbons, where the pipe section is configured to be screwed on or off an adjoining expandable pipe section, the pipe section at one end being provided with a male end having externally arranged threads and where the adjoining expandable pipe section is provided with a correspondingly shaped female end having corresponding internal threads. The distance between adjacent threads at their widest point is less than the maximum width of a thread. Those parts of the pipe being provided with threads are provided with at least two step wise arranged parts with a cylindrical surface being coaxially arranged with the pipe wall(s).