Offshore Riser Keel Guide for Fatigue Reduction
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Solution Overview
Problem
Steel catenary risers on offshore platforms experience significant fatigue damage due to global motions like roll, pitch, and yaw, which are amplified by their attachment points at the perimeter of the platform, leading to reduced fatigue life.
Innovation Solution
A keel guide structure is designed to support steel catenary riser porches closer to the center of rotation, incorporating a deep box-section structure that adds effective water mass and accommodates additional loading, reducing motion-induced displacements and fatigue damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If riser porches are attached at the outer perimeter of the platform, then the platform structure is simplified and easier to manufacture, but the fatigue damage to riser components increases due to amplified global motions
Solution Approach 1:
The patent introduces a new spatial dimension by mounting riser porches on the keel guide structure at the centerline of the platform, rather than at the traditional peripheral locations. This dimensional repositioning moves the attachment points from the outer perimeter (where they experience amplified motions) to the central region (where global motions are minimal), thereby reducing fatigue damage while maintaining structural simplicity
Solution Approach 2:
The keel guide structure serves as an intermediary element that enables the riser porches to be positioned at the centerline. This intermediate structure mediates between the conflicting requirements by providing a mounting platform at the optimal location (centerline) without requiring complex modifications to the existing platform hull structure
2Reliability
If riser porches are moved closer to the center of rotation, then fatigue damage is reduced, but the platform structure becomes more complex requiring additional support structures
Solution Approach 1:
The keel guide structure is designed to serve multiple functions: it provides structural support for the riser porches, acts as a mounting platform for equipment, and serves as a load-bearing element for top tensioned risers. By making the keel guide multi-functional, the patent avoids the need for additional dedicated support structures, thereby reducing overall system complexity while still achieving the fatigue reduction benefit of centralised porch locations
3Reliability
If a deep box-section keel guide structure is used to support inboard porches, then fatigue life is extended, but the weight of the platform structure increases
Solution Approach 1:
The patent specifies that the keel guide structure be constructed from high-strength steel materials that provide superior strength-to-weight ratio compared to conventional materials. This allows the structure to achieve the required load-bearing capacity and fatigue resistance for supporting inboard porches while minimizing the weight penalty through optimized material selection rather than simply increasing structural dimensions
Data Source
AI summary
A floating, offshore drilling and/or production vessel has supports for steel catenary risers mounted on a riser keel guide. This allows the riser attachment points to be located closer to the vessel's center(s) of rotation of pitch, roll and yaw thereby decreasing roll-, pitch- and yaw-induced displacements of the risers.