Steel Riser Termination Bearing Structure for FPSO Bending Relief
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Solution Overview
Problem
Existing rigid steel risers are not adapted to be coupled to I-tube coupling interfaces on floaters, leading to excessive cyclic bending stresses due to bending moment constraints, which can result in fatigue damage and increased corrosion risks.
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 and an upper hang-off seat, along with a termination conduit with a bearing structure and variable cross-section, allowing the riser to bend naturally and reduce stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If rigid steel risers are coupled to I-tube coupling interfaces on floaters, then the connection strength and stability are improved, but excessive cyclic bending stresses occur due to bending moment constraints
Solution Approach 1:
The riser is divided into multiple sections with different cross-sectional properties. The upper part has a larger cross-section for strength, while the lower part has a smaller cross-section to reduce bending stiffness and allow natural bending, thereby reducing cyclic bending stresses at the connection interface.
Solution Approach 2:
The riser structure is optimized locally at different positions. The upper section near the connection interface has enhanced structural properties for strength, while the lower section has reduced bending stiffness to accommodate movement and reduce stress concentrations, creating different local qualities along the riser length.
2Stability of the object's composition
If rigid steel risers are coupled to I-tube coupling interfaces, then structural stability is improved, but fatigue damage and corrosion risks increase
Solution Approach 1:
The riser design incorporates dynamic characteristics by allowing controlled bending and movement in the lower section. This dynamic capability enables the riser to adapt to floating unit movements, reducing cyclic stress accumulation and improving fatigue resistance while maintaining overall structural stability.
Solution Approach 2:
The riser employs composite construction with different material properties in different sections. The upper section uses high-strength materials for structural stability, while the lower section uses materials with appropriate flexibility and corrosion resistance, creating a composite structure that balances stability and reliability.
3Ease of manufacture
If uniform cross-section rigid steel risers are used, then manufacturing simplicity is maintained, but stress concentrations occur at connection points
Solution Approach 1:
The riser structure is optimized locally at different positions. The upper section near the connection interface has enhanced structural properties for strength, while the lower section has reduced bending stiffness to accommodate movement and reduce stress concentrations, creating different local qualities along the riser length.
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 effectively reduces lateral loads and bending stresses on the riser and I-tube connection interface, preventing excessive stress levels and fatigue damage, while also improving safety and reducing costs by utilizing structural steel conduits.
Implementation Method 1
an annular rounded bearing body (36) having a bearing body diameter (37) and protruding outward from said termination conduit (28) inside said bearing seat (33), wherein the bearing body diameter (37) is smaller than the bearing seat diameter (34) to provide an at least unilateral gap (46) between the bearing body (36) and the bearing seat (33) and allow relative axial sliding along the bearing seat axis (35) and relative rotation at least about the bearing seat axis (35) between the bearing body (36) and the bearing seat (33)
Data Source
AI summary
A riser termination connecting a steel riser duct to an I-tube or J-tube connecting interface of a floating unit has an upper hang off portion, lower coupling adapter, steel termination conduit having an upper conduit end rigidly connected to the upper hang off portion, and lower conduit end connected to an adjacent conduit section of the riser duct. The termination conduit extends axially slidable through the coupling adapter. A cylindrical bearing seat inside the coupling adapter defines a bearing seat diameter and axis. An annular rounded bearing body has a bearing body diameter and protrudes outward from the termination conduit inside the bearing seat, the bearing body diameter being smaller than the bearing seat diameter to provide a unilateral gap and allow relative axial sliding and rotation. The termination conduit includes a variable cross-section portion having an external diameter and wall thickness tapering from the bearing body.