Subsea Riser Installation Using Piggybacked Flexible Conduits
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Solution Overview
Problem
The installation of subsea risers is complex and time-consuming, particularly in dynamic environments, leading to high costs and risks of missing weather windows, due to the fatigue-induced failure of conventional rigid pipes in challenging sea conditions.
Innovation Solution
A method involving the piggybacking of riser conduits onto elongate supports, such as pipeline bundles, where the conduits are detached at the seabed and lifted to a riser support near the surface, allowing for fluid communication through intermediate couplings, and utilizing flexible or composite pipes to reduce fatigue and simplify installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rigid pipes are used for subsea risers, then structural strength is maintained, but fatigue-induced failure occurs in dynamic environments with high sea states and strong currents
Solution Approach 1:
The patent changes the material parameter from rigid steel to flexible composite materials, allowing the riser to dynamically adapt to environmental loads while maintaining structural integrity. The flexible pipe construction with multiple layers (polymer liner, steel wire braid, polymer outer layer) provides both flexibility and strength, resolving the contradiction between rigidity and fatigue resistance.
Solution Approach 2:
The patent employs composite materials consisting of polymer liners, steel wire braids, and polymer outer layers to create a flexible riser that combines the advantages of different materials. The steel wire braid provides tensile strength while the polymer layers provide flexibility and corrosion resistance, eliminating fatigue failures while maintaining structural strength.
2Ease of manufacture
If free-hanging rigid risers are installed, then installation simplicity is achieved, but installation time increases due to complex positioning and tensioning requirements
Solution Approach 1:
The patent uses a towing assembly with buoyancy modules attached beforehand to the flexible riser. This preliminary action allows the riser to be self-supported during towing and deployment, eliminating the need for complex vessel equipment and multiple installation vessels, thereby reducing installation time while maintaining simplicity.
Solution Approach 2:
The flexible riser with integrated buoyancy modules is self-supported during towing and deployment operations. The buoyancy modules provide natural floatation, allowing the riser to support itself without external assistance, reducing the need for complex positioning equipment and reducing installation time.
3Adaptability or versatility
If multiple separate installation operations are performed for flowlines and risers, then installation flexibility is maintained, but vessel time costs increase and weather window risks increase
Solution Approach 1:
The patent merges the flowline and riser installation operations into a single towing and deployment action. The flexible riser is piggybacked on the flowline during towing, and both are deployed simultaneously to the seabed location, eliminating the need for separate installation operations and reducing vessel time while maintaining flexibility through the flexible pipe construction.
Data Source
AI summary
A subsea riser is installed by lowering at least one riser conduit to the seabed when piggybacked to an elongate support that comprises at least one flowline. The elongate support may be a pipeline bundle, which may be attached to one or more towheads in a towable bundle unit. The riser conduit may be in fluid communication with the flowline. At the seabed, a free end portion of the riser conduit is detached from the elongate support by releasing subsea-releasable fastenings. Then, with the elongate support and a root end of the riser remaining at the seabed, the detached free end portion of the riser conduit is lifted away from the elongate support to a riser support, such as a platform, an FPSO (floating production, storage and offloading vessel), or a buoy.