Riser Coupling System with Independent Pull and Clamping Connectors
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Solution Overview
Problem
Existing coupling systems between risers and underwater supporting structures in offshore oil and gas extraction face challenges in managing mechanical stresses, particularly at the lower interface, where a balance between flexibility to absorb movements and structural integrity is needed, while also minimizing the size, weight, and cost of the supporting structure.
Innovation Solution
A coupling system comprising a coupling seat and head with a pull connector for provisional connection and a clamping connector for complete clamping, allowing rotation and preventing translation, which reduces stress during engagement and fatigue, and can be actuated independently to avoid structural oversizing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a rigid clamping anchoring of the lower end portion of the riser in the base foundation is used, then movements of the end portion are reduced and strain peaks are minimized, but the base foundation becomes very rigid, massive and large, increasing construction cost and time
Solution Approach 1:
The coupling system is divided into two independent functional components: a pull connector that handles axial tension forces and a clamping connector that handles transverse movements and rotations. This segmentation allows each component to be optimized for its specific function, enabling the base foundation to be smaller while still providing reliable stress management during installation and operation.
Solution Approach 2:
The coupling system transitions from a static rigid connection to a dynamic system that adapts to different operational phases. During installation, the pull connector allows controlled movement to reduce strain peaks. During operation, the clamping connector provides stability while accommodating thermal expansion and contraction, allowing the base foundation to be smaller without compromising reliability.
2Strength
If a rigid, massive and large base foundation is constructed to reduce movements during engagement, then strain peaks are reduced, but construction cost and time increase significantly
Solution Approach 1:
The pull connector is designed to be activated first during the engagement process, preliminarily securing the riser to the base foundation in a controlled manner. This preliminary action allows the system to manage stresses during the critical engagement phase without requiring an oversized foundation, thereby reducing construction cost and time while maintaining strength.
Solution Approach 2:
The coupling system changes its mechanical parameters dynamically: during engagement, it provides high stiffness through the pull connector to manage stress peaks; during operation, it allows controlled flexibility through the clamping connector to accommodate thermal and mechanical variations. This parameter change enables a smaller, more cost-effective base foundation design.
3Ease of manufacture
If a simpler and therefore stiffer serpentine interface is used, then manufacturing and installation are easier, but stress peaks occur due to impeded movements of the riser
Solution Approach 1:
The serpentine interface is segmented into multiple flexible sections rather than being a single continuous structure. This segmentation allows each section to independently accommodate movements, reducing stress peaks while maintaining manufacturing simplicity. The segmented design provides flexibility without requiring a complex single-piece interface.
Solution Approach 2:
The serpentine interface utilizes flexible metallic sections that can bend and deform to accommodate riser movements. These flexible sections are designed with appropriate thickness and geometry to provide the necessary flexibility while maintaining structural integrity, thereby reducing stress peaks without complicating manufacturing.
4Reliability
If the pull connector and clamping connector are actuated independently, then complete clamping can be postponed to avoid excessive stresses during engagement, but the system complexity increases
Solution Approach 1:
The actuation system is segmented into two independent control mechanisms: one for the pull connector and another for the clamping connector. This segmentation allows sequential actuation where the pull connector is activated first to secure the riser with minimal stress, and the clamping connector is activated later to provide full constraint. While this increases device complexity, it enables stress reduction during engagement, improving overall reliability.
Solution Approach 2:
The pull connector is actuated in advance during the engagement phase to secure the riser to the base foundation in a controlled, low-stress manner. The clamping connector is postponed for actuation until after the riser is properly positioned and initial stresses are managed. This preliminary action sequence reduces engagement stresses while the independent actuation mechanisms manage the system complexity.
Data Source
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AI summary
A coupling system (12) between a riser (2) and an underwater supporting structure (10), comprises a coupling seat (13) and a coupling head (14) which can be inserted in the seat, a pull connector (16), which constrains the head (14) to the seat (13) so as to prevent the extraction of the head (14) but to allow rotations of the head (14), a clamping connector (18), which constrains the head (14) to the seat (13) so as to prevent transversal translations and rotations to the head (14) and the seat (13), wherein the pull connector (16) can be actuated alone and independently from the clamping connector (18) to make a provisional, pull-only connection between the head (14) and the coupling seat (13), wherein the clamping connector (18) can be actuated independently from the pull connector (16) to allow postponing the complete clamping with respect to the provisional connection.