Tapered Metal-Composite Riser Interface
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Solution Overview
Problem
Existing metal/composite interfaces in risers for offshore oil and gas production face limitations in ultimate strength due to stress concentration at specific positions under increasing axial compressive or tensile loads, particularly in deeper water operations where risers must withstand greater loads.
Innovation Solution
A composite riser design featuring a tubular metal liner with external grooves containing a composite hoop structure and axial fibers secured by hoop or helical fibers, which distributes loads more evenly across the metal/composite interface, enhancing the strength and reducing stress concentrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If traditional metal/composite interfaces are used in risers, then the structure can be assembled with standard fittings, but stress concentration occurs at specific positions under axial loads, limiting ultimate strength
Solution Approach 1:
The invention applies local quality by creating a tapered interface region with gradually varying geometry and material properties. The metal connector transitions from a larger diameter at the metal end to a smaller diameter at the composite end, creating a gradient structure that locally adapts to stress distribution patterns. This tapered geometry concentrates material where stresses are highest and reduces material where stresses are lower, thereby eliminating stress concentration points while maintaining overall structural integrity.
Solution Approach 2:
The invention employs composite materials by combining metal and composite materials in a tapered interface structure. The metal connector features a tapered region where metal material gradually transitions to composite material, creating a hybrid structure that leverages the high strength of metal and the corrosion resistance/lightweight properties of composites. This composite approach allows the interface to distribute stresses more evenly across the transition zone, preventing stress concentration.
2Length of moving object
If riser length is increased for deeper water operations, then the riser can reach deeper wells, but the axial tension and compressive loads increase significantly
Solution Approach 1:
The invention uses composite materials to construct the riser, combining metal liners or connectors with composite material jackets. This composite construction provides high strength-to-weight ratio, enabling the riser to withstand the increased axial tension and compressive loads associated with greater lengths while maintaining acceptable weight characteristics for installation and operation.
Solution Approach 2:
The tapered interface structure applies local quality by concentrating enhanced structural properties at the metal/composite transition zone where stress concentrations occur. The gradual geometric transition in the tapered region provides localized reinforcement that prevents failure initiation under high axial loads, allowing the overall riser structure to support greater lengths and corresponding loads.
3Weight of moving object
If the metal connector diameter is reduced to decrease weight, then weight is reduced, but the load-bearing capacity at the interface is compromised
Solution Approach 1:
The invention uses composite materials to compensate for the reduced metal connector diameter. The composite material jacket provides additional load-bearing capacity that compensates for the smaller metal section, allowing weight reduction while maintaining or enhancing overall load-bearing capacity. The composite material's high strength-to-weight ratio enables this trade-off.
Solution Approach 2:
The tapered interface structure applies local quality by creating a geometric gradient that optimizes stress distribution throughout the connector. The gradual transition in diameter ensures that stress concentrations are eliminated, allowing the connector to maintain high load-bearing capacity despite reduced overall dimensions and weight. The local geometric adaptation compensates for the reduced cross-sectional area.
Data Source
AI summary
The invention relates to improved metal/composite interfaces, particularly for risers used in offshore oil and gas production to connect a subsea oil well to a surface drilling/production facility. The invention provides a composite hoop structure configured to a bearing surface of a metal groove of metal liner over which axial fibers are laid. The composite hoop structure provides for improved transition of axial, torsional and compressive forces between composite fibers and metal surfaces of the metal liner.