Threaded Tubular Connection Fatigue Resistance via Radial Load Redirection
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Threaded connections in tubular elements, especially in drillpipe strings and offshore platforms, face fatigue issues due to stress variations leading to micro-cracks at thread roots, compromising their resistance and causing disengagement or failure under variable loads.
Innovation Solution
The design modifies radial load transfer zones to be positioned at a radial distance from the thread roots, forming an angle of less than 40° with the axis, using features like helical protuberances and ramps on the thread flanks to redirect load transfer away from high-stress areas, reducing tensile stress impact on the thread roots.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If radial load transfer zones are positioned at thread crest and root contact zones, then radial interference is achieved and connection monolithic structure is improved, but micro-cracks form at thread roots under variable tensile stresses, compromising fatigue resistance
Solution Approach 1:
The invention extracts the radial load transfer function from the thread root contact zone by positioning the radial load transfer zones on the thread flanks at a radial distance from the thread roots. This separates the load transfer function from the high-stress thread root area, preventing micro-crack formation while maintaining connection stability through radial interference between threaded elements
Solution Approach 2:
The invention transitions the radial load transfer zones from a conventional axial position at thread crest-root contact to a radial position on the thread flanks. By forming angles of less than 40° with the axis (compared to conventional 60° load flanks), the load transfer occurs in a different spatial orientation that avoids the high-tensile-stress region at the thread roots
2Strength
If thread depth is increased with triangular threads to prevent disengagement, then connection strength is improved, but thread roots experience higher tensile stresses under variable loads, leading to fatigue cracking
Solution Approach 1:
The invention applies different functional qualities to different regions of the thread structure. The thread roots are designed with larger radii of curvature to reduce stress concentration, while the radial load transfer zones are positioned on the flanks to handle radial loads. This local differentiation allows the thread roots to avoid high tensile stresses while maintaining overall connection strength
3Force
If load flanks are positioned at 60° to the axis, then radial interference and load transfer are achieved, but tensile stresses at thread roots remain high under variable axial loads, causing fatigue failure
Solution Approach 1:
The invention changes the angular parameter of the load transfer zones from the conventional 60° load flanks to zones forming angles of less than 40° with the axis. This parameter change repositions the radial load transfer zones to a location where they can effectively transfer radial loads through radial interference while being radially separated from the thread roots, thereby reducing the tensile stresses that cause fatigue failure
Data Source
AI summary
A method to improve fatigue resistance of a threaded tubular connection. Radial interference between a male and female threading operates between stabbing flanks inclined at about 27° with respect to an axis of the threadings, wherein mutual contacting surfaces are radially spaced from a root of the male threading, which is defined by a concave rounded portion.