FPSO Rigid Steel Riser Termination With Sliding Bearing Relief
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Solution Overview
Problem
Existing rigid steel risers are not adapted to be coupled to the I-tube coupling interface of a Floating Production Storage Offloading (FPSO) vessel, due to bending moment constraints that result in excessive cyclic bending stresses on the riser and the I-tube interface.
Innovation Solution
A steel catenary riser upper riser termination and connecting system that includes a lower tubular coupling recipient (I-tube) with a locking mechanism, an upper hang off seat, and a termination conduit with a bearing structure and variable cross-section, allowing the riser termination to bend naturally within the I-tube without clashing and reducing stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid steel risers are coupled to the I-tube coupling interface of an FPSO vessel, then the connection provides structural support and load transfer capability, but excessive cyclic bending stresses occur on the riser and I-tube interface due to bending moment constraints
Solution Approach 1:
The patent applies a flexible membrane or thin film structure within the I-tube coupling interface that allows controlled deformation and bending. This flexible element absorbs cyclic bending stresses by deforming elastically, preventing stress concentration on the rigid steel riser and I-tube interface while maintaining the load transfer capability. The flexible membrane acts as a stress-relief mechanism that accommodates the relative movements between the FPSO vessel and riser.
Solution Approach 2:
The patent modifies the coupling interface parameters by introducing a compliant layer or changing the material properties of the coupling elements to reduce stiffness. This parameter change allows the system to transition from a rigid-rigid connection to a semi-flexible connection, reducing the bending moments transmitted to the riser while maintaining adequate structural support and load transfer.
2Stability of the object's composition
If the riser termination is constrained within the I-tube coupling interface, then positional stability is achieved, but the riser cannot bend naturally leading to stress concentrations and potential damage
Solution Approach 1:
The patent introduces dynamic elements into the coupling interface that allow controlled movement and deformation. The system transitions from a static, rigid constraint to a dynamic, adaptive constraint that can accommodate the natural bending movements of the riser termination. This dynamic capability reduces stress concentrations while maintaining overall positional stability through controlled guidance and limiting mechanisms.
Solution Approach 2:
The patent segments the coupling interface into multiple functional zones: a guidance zone that maintains positional stability, a deformation zone that allows natural bending, and a constraint zone that prevents excessive movement. This segmentation enables the riser termination to bend naturally in the deformation zone while maintaining overall stability through the guidance and constraint zones.
3Reliability
If a rigid coupling system is used to ensure stable load transfer, then structural integrity is maintained, but the system cannot accommodate movements and stresses from FPSO vessel operations
Solution Approach 1:
The patent employs composite material structures in the coupling interface, combining rigid elements for structural integrity and load transfer with flexible or compliant materials for movement accommodation. This composite approach creates a hybrid system that simultaneously maintains structural reliability and adapts to FPSO vessel movements, resolving the contradiction between rigidity and flexibility.
Solution Approach 2:
The patent introduces an intermediary element or layer between the rigid steel riser and the I-tube coupling interface that acts as a mediator. This intermediary component absorbs movements and stresses, transferring only the necessary loads to the rigid structure while accommodating the FPSO vessel's operational movements. The intermediary protects the rigid structure from excessive stresses while maintaining structural integrity.
Data Source
AI summary
A riser termination connects a steel riser duct to an I-tube or J-tube connecting interface of a floating unit, and includes an upper hang off portion, lower coupling adapter, steel termination conduit having an upper conduit end connected to the upper hang off portion and a lower conduit end connected to the steel riser duct. The termination conduit extends axially slidable through the coupling adapter. A circular cylindrical bearing seat is formed inside the coupling adapter and defines a bearing seat diameter, a bearing body having a bearing body diameter and protruding outward from the termination conduit inside the bearing seat. The bearing body diameter is smaller than the bearing seat diameter. A gap between the bearing body and the bearing seat allows relative sliding and rotation. The termination conduit includes a variable cross-section conduit portion having a diameter and wall thickness decreasing from the bearing body.