Flexible Riser Buoyancy Layout for Overbending Control
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Solution Overview
Problem
In deep and ultra-deep water environments, flexible pipes used for transporting production fluids face high tension loads due to internal pressure and self-weight, leading to potential failure, especially at the hang-off region, and existing buoyancy solutions may not adequately manage vessel motion-induced curvature changes and overbending.
Innovation Solution
A riser assembly with a mid-line buoyancy section and two distributed buoyancy sections, where the mid-line section is formed by connecting buoyancy compensating elements in an in-line configuration, and the distributed sections are positioned above to maintain tension loads and support the riser in a wave configuration, reducing bending and fatigue.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If buoyancy aids are provided at discrete locations along the riser, then installation cost and installation time are reduced, but the riser may still experience overbending and curvature changes due to vessel motion
Solution Approach 1:
The riser is divided into multiple sections with buoyancy aids positioned at specific intervals. The riser includes a first section with a first buoyancy aid, a second section with a second buoyancy aid, and a third section with a third buoyancy aid, creating segmented buoyancy zones that control different portions of the riser independently
Solution Approach 2:
Different sections of the riser are given different buoyancy characteristics. The first buoyancy aid has a first buoyancy force, the second buoyancy aid has a second buoyancy force, and the third buoyancy aid has a third buoyancy force, where each buoyancy force is specifically tailored to control the local configuration and tension in its respective section
2Productivity
If buoyancy aids are provided at discrete locations along the riser, then installation time is reduced, but the riser may still experience overbending and curvature changes due to vessel motion
Solution Approach 1:
The riser is divided into multiple sections with buoyancy aids positioned at specific intervals. The riser includes a first section with a first buoyancy aid, a second section with a second buoyancy aid, and a third section with a third buoyancy aid, creating segmented buoyancy zones that control different portions of the riser independently
Solution Approach 2:
Different sections of the riser are given different buoyancy characteristics. The first buoyancy aid has a first buoyancy force, the second buoyancy aid has a second buoyancy force, and the third buoyancy aid has a third buoyancy force, where each buoyancy force is specifically tailored to control the local configuration and tension in its respective section
3Strength
If traditional flexible pipe is used without buoyancy aids, then the pipe structure must withstand high tension loads, but this increases the risk of failure at the hang-off region
Solution Approach 1:
Buoyancy aids are attached to the riser to provide upward buoyant forces that counteract the downward gravitational force and reduce the tension load on the pipe. The first buoyancy aid provides a first upward buoyant force, the second buoyancy aid provides a second upward buoyant force, and the third buoyancy aid provides a third upward buoyant force, collectively reducing the net tension at critical locations
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 solution effectively maintains the riser in a suitable configuration, minimizing overbending and fatigue, while being cost-effective and easy to assemble, thus improving performance in extreme conditions.
Implementation Method 1
The buoyancy compensating elements are provided along the riser in an arrangement to help provide bending support where needed and maintain the riser in a suitable configuration in a sub-sea environment
Data Source
Figure 1~2b
Figure 3~4
Figure 5
AI summary
A riser assembly (500) for transporting fluids from a sub-sea location is disclosed. The riser assembly (500) includes a riser (501) having at least one segment of flexible pipe and a plurality of buoyancy compensating elements (511) connected to the riser (501) and connected together in an in-line configuration to form a mid-line buoyancy section (510). The riser assembly (500) also includes at least one buoyancy aid (521) connected to the riser (501) at a position above and spaced apart from the mid-line buoyancy section (510). The at least one buoyancy aid (521) forms a first distributed buoyancy section (520) and is sufficiently buoyant to maintain a tension load on the riser (501) between the first distributed buoyancy section (520) and the mid-line line buoyancy section (510). The riser assembly (500) further includes at least one further buoyancy compensating element (531) connected to the riser (501) at a position above and spaced apart from the first distributed buoyancy section (520) to form a second distributed buoyancy section (530). The second distributed buoyancy section (530) is configured to support a portion of the riser (501) in a wave configuration.