Articulated Subsea Riser Link for Fatigue Motion Decoupling
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Solution Overview
Problem
Conventional subsea riser systems, particularly free-hanging rigid risers, are susceptible to fatigue-induced failure due to dynamic motion from vessels and environmental factors, leading to high maintenance costs and potential rupture, especially in challenging environments like high sea states and strong currents.
Innovation Solution
An articulated pliant link comprising a longitudinal series of interconnected rigid segments surrounding a pliant pipe, which decouples the riser from vessel motion and allows limited relative motion, thereby reducing stress and fatigue, is integrated between the upper and lower sections of the riser, enabling flexible installation methods such as S-lay or reel-lay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rigid steel risers are used, then structural strength and load-bearing capacity are improved, but susceptibility to fatigue-induced failure from dynamic motion increases
Solution Approach 1:
The riser is divided into multiple rigid pipe sections connected by articulated joints with universal hinges, creating a segmented structure that combines rigidity with flexibility to reduce fatigue from dynamic motion
Solution Approach 2:
The riser transitions from a static rigid structure to a dynamic articulated structure capable of relative motion at joints, allowing the system to adapt to environmental movements and reduce stress accumulation
2Strength
If rigid pipe sections are connected by welding, then structural integrity is improved, but installation flexibility and ease of assembly deteriorate
Solution Approach 1:
The riser is divided into modular rigid pipe sections that can be manufactured separately and assembled through articulated joints, enabling flexible installation methods such as S-lay or reel-lay while maintaining structural integrity
Solution Approach 2:
Articulated joints with universal hinges serve as intermediary connection elements between rigid pipe sections, providing mechanical coupling that allows flexible installation while maintaining load-bearing capacity
3Adaptability or versatility
If the riser is made fully flexible, then adaptability to dynamic motion is improved, but load-bearing capacity and structural strength deteriorate
Solution Approach 1:
The riser uses segmented rigid sections rather than a continuous flexible structure, maintaining load-bearing capacity through rigid segments while achieving adaptability through articulated joints between segments
Solution Approach 2:
The riser employs a composite structure combining rigid pipe sections with articulated joint mechanisms, integrating the strengths of both rigid and flexible systems to achieve simultaneous load-bearing capacity and motion adaptability
4Device complexity
If minimal joints are used in the riser, then structural simplicity is improved, but ability to decouple from vessel motion deteriorates
Solution Approach 1:
The riser incorporates articulated joints with universal hinges that enable relative motion between sections, providing dynamic adaptability to decouple from vessel motion while maintaining relatively simple structural configuration
Data Source
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Figure 6a~6d
AI summary
A pliant link to mitigate fatigue-inducing motion of a subsea catenary riser comprises an articulated spine having a longitudinal series of interconnected rigid segments. The spine can be coupled to upper and lower sections of the riser to transmit loads along the riser through the link on a load path that extends through the segments. The link also comprises a pliant pipe terminating in end fittings that can be joined, respectively, to the upper and lower sections of the riser for fluid communication along the riser through the link.