Subsea Catenary Riser Buoy Decoupling for Fatigue Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional steel catenary risers (SCRs) are susceptible to fatigue-induced failure due to direct transmission of motion from floating upper supports to the seabed, especially in dynamic environments with high sea states and strong currents, leading to increased costs and complexity in riser systems.
Innovation Solution
A subsea riser system that includes a rigid riser pipe suspended as a catenary from a floating support, with a toroidal buoy attached to the riser above the sagbend, allowing rotation and sliding movements relative to the riser. This configuration decouples the riser from the motion of the supporting vessel, reducing fatigue and top tension.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a free-hanging rigid riser is used, then installation cost and complexity are reduced, but fatigue resistance deteriorates due to direct motion transmission from floating support to seabed
Solution Approach 1:
A buoyant body is introduced as an intermediary element between the floating support and the riser. This buoyant body decouples the motion transmission path, allowing the riser to remain relatively stationary while the buoyant body absorbs and isolates the dynamic motions from waves, currents, and platform movement, thereby preventing fatigue damage without requiring complex alternative riser configurations
2Reliability
If multiple buoyancy modules are added to reduce fatigue, then fatigue resistance improves, but device complexity and installation cost increase
Solution Approach 1:
Multiple buoyancy functions are merged into a single integrated buoyant body. Instead of distributing multiple separate buoyancy modules along the riser, the invention consolidates the buoyancy capability into one unified structure that performs all necessary motion decoupling functions, thereby achieving fatigue protection while minimizing system complexity and installation requirements
3Device complexity
If a single buoyant body is used, then device complexity is reduced and installation cost decreases, but motion decoupling effectiveness may be insufficient
Solution Approach 1:
The buoyant body is designed with dynamic characteristics that enable effective motion decoupling. It is configured to move independently in response to external forces such as waves and currents, allowing it to absorb and isolate dynamic motions while maintaining its buoyancy function. This dynamic behavior ensures that a single buoyant body can effectively decouple riser motion without requiring multiple modules
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 proposed solution effectively reduces fatigue and top tension in the riser, improves dynamic behavior, and lowers installation costs by eliminating the need for multiple buoyancy modules, while allowing conventional installation techniques.
Implementation Method 1
a buoyant body is spaced radially from the inner part
Implementation Method 2
The joint allows the riser pipe to rotate relative to the buoy about mutually orthogonal, substantially horizontal axes
Data Source
Figure 1
Figure 2
Figure 3
AI summary
A subsea catenary riser comprises a rigid riser pipe that is suspended from a floating support on the surface and extends through a sagbend to the seabed. A hang-off interface allows rotation or pivoting of the riser pipe relative to the support about mutually orthogonal horizontal axes. A subsea buoy is positioned on the riser pipe above the sagbend. The buoy applies buoyant upthrust force to the riser pipe via an attachment interface that allows rotation or pivoting of the riser pipe relative to the buoy about mutually orthogonal horizontal axes. In response to movement of the support, the riser pipe deflects with S-shaped curvature to vary the inclination, relative to the buoy, of the portion of the riser pipe to which the buoy is attached. The curvature comprises mutually opposed curves respectively above and below the buoy, joined by a region of inflection that coincides with the buoy.