Subsea Catenary Riser Buoy Interface for Fatigue Reduction
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional rigid subsea risers, such as steel catenary risers, are susceptible to fatigue-induced failure due to motion from floating supports like FPSOs, especially in dynamic environments with high sea states and strong currents, leading to increased costs and complexity in installation and maintenance.
Innovation Solution
A subsea riser system with a rigid riser pipe suspended from a surface support, featuring a hang-off interface allowing rotation about orthogonal axes and a subsea buoy above the sagbend that applies buoyant upthrust force, enabling S-shaped curvature deflection to decouple motion and reduce fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a free-hanging rigid riser is used, then installation cost and complexity are reduced, but fatigue-induced failure risk increases due to motion transmission from floating supports
Solution Approach 1:
A subsea buoy is introduced as an intermediary element between the floating support and the riser. The buoy applies buoyant upthrust force to the riser and is attached via an interface allowing rotation about orthogonal axes, decoupling motion transmission and reducing fatigue on the riser while maintaining the simplicity of free-hanging installation
Solution Approach 2:
The subsea buoy provides buoyant upthrust force that counteracts the weight and top tension of the riser. This reduces the net downward force on the riser, decreasing the tension load at the top and reducing fatigue-induced failure risk while maintaining structural integrity
2Reliability
If additional buoyancy modules are added to reduce top tension, then reliability improves, but device complexity and installation cost increase
Solution Approach 1:
The buoyancy function and the motion decoupling function are merged into a single subsea buoy element. This buoy provides both the buoyant upthrust force to reduce top tension and the rotational attachment interface to decouple motion, eliminating the need for separate buoyancy modules and reducing overall system complexity
Solution Approach 2:
The subsea buoy serves multiple functions simultaneously: it provides buoyant support to reduce top tension, decouples motion from the floating support through rotational degrees of freedom, and maintains riser positioning. This multi-functionality reduces the number of components needed while achieving reliability improvements
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 system reduces fatigue and top tension, lowers installation costs, and allows conventional installation methods, providing a cost-effective solution for dynamic environments without the need for additional buoyancy modules.
Implementation Method 1
A subsea buoy positioned on the riser pipe above the sagbend applies buoyant upthrust force
Data Source
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.