Threaded Tubular Connection With Undulated Transfer Zone
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Solution Overview
Problem
Threaded tubular connections in offshore well strings face dynamic bending loads, leading to fatigue cracking and fretting fatigue due to uneven stress distribution and friction, with existing solutions insufficiently addressing these issues and increasing costs through thicker tubes or local thickening.
Innovation Solution
A threaded connection with a transfer zone between the threaded portions and the free end of one tubular element, featuring undulated transfer surfaces with a radial interference fit, which distributes at least 20% of the bending moment and includes features like lubrication and sealing surfaces to reduce stress and prevent cracking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If axial abutment surfaces are formed to absorb bending moment, then bending load resistance is improved, but tube thickness must be increased or local thickening by upsetting must be applied, leading to increased costs
Solution Approach 1:
The connection interface is segmented into multiple functional zones: a threaded portion for axial load transmission and an axially spaced transfer zone for bending moment transfer. This segmentation allows each zone to optimize its function without compromising the other, eliminating the need for thickened tubes or upsetting while maintaining bending load resistance.
Solution Approach 2:
The invention transitions from a single-plane abutment contact to a distributed transfer zone with undulated surfaces extending in the radial dimension. The undulated transfer surfaces create multiple contact points (ridges and valleys) that collectively absorb bending moments, replacing the need for increased tube thickness with a multi-dimensional contact interface.
2Force
If threaded portions are designed to transmit axial tensile loads, then load transmission is improved, but the last threads are subjected to maximum bending moment and dynamic tensile loads, initiating fatigue cracking
Solution Approach 1:
The load transmission function is segmented between two distinct zones: the threaded portion handles axial tensile loads while the axially spaced transfer zone handles bending moments. This spatial separation prevents the concentration of both axial and bending stresses at the thread roots, eliminating the primary mechanism for fatigue cracking initiation.
Solution Approach 2:
The transfer zone with undulated surfaces acts as an intermediary element between the threaded portion and the tube ends. It mediates the bending moment transmission by distributing stresses across multiple contact points, preventing direct stress concentration at the vulnerable thread root locations.
3Strength
If undulated transfer surfaces with radial interference fit are used to distribute bending loads, then bending moment distribution is improved, but contact pressure must be controlled to remain below yield strength
Solution Approach 1:
The contact interface is segmented into multiple discrete contact points along the undulated surfaces rather than a continuous contact. This segmentation distributes the bending moment across numerous ridges and valleys, reducing the contact pressure at each individual point while maintaining overall load transmission capability.
Solution Approach 2:
The undulated transfer surfaces incorporate curved ridge and valley profiles that naturally distribute contact pressures. The rounded geometry of the undulations allows for stress distribution across broader contact areas, preventing localized pressure concentrations that could exceed yield strength while still effectively transferring bending moments.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution effectively reduces fatigue and fretting fatigue by distributing bending loads, maintaining a seal, and housing debris, thereby enhancing the durability and reliability of the threaded tubular connections under dynamic loads.
Implementation Method 1
the male and female elements having respective transfer surfaces in mutual contact with a radial interference fit in said transfer zone
Implementation Method 2
said male and female transfer surfaces are lubricated
Data Source
AI summary
A threaded tubular connection includes a male tubular element including a male threaded portion and a female tubular element including a female threaded portion that cooperates by screwing with the male threaded portion. The threaded connection includes at least one transfer zone that can transfer bending loads between the elements and that is axially spaced from the threaded portions, in which the male and female elements have an undulating surface and a smooth surface facing each other, the undulating surface defining a series of rounded annular ribs that come into contact with the smooth surface with a radial interference fit. The connection may find application to production strings for hydrocarbon wells.