Steel Catenary Riser Ballasted Curvature Loops for Fatigue Life
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Solution Overview
Problem
Conventional steel catenary risers (SCRs) experience fatigue failure due to repetitive motion from floating upper supports and sea conditions, leading to potential rupture, especially in harsh environments, while alternative flexible risers are costly and complex to install.
Innovation Solution
Implement a method of installing SCRs using the residual curvature method (RCM) to form pre-bent loops with attached ballast weights, enhancing the riser's dynamic response and reducing fatigue by absorbing compression and tension motions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If conventional steel catenary risers are used with standard straightening, then installation is simpler and cost is lower, but fatigue resistance deteriorates due to high dynamic loads and compression waves at the touch-down point
Solution Approach 1:
The riser is pre-formed with residual curvature loops during the straightening process before installation. This preliminary action creates loops with specific curvature radii that will absorb compression waves and reduce dynamic loads during operation, improving fatigue resistance without requiring complex installation procedures
Solution Approach 2:
Instead of uniformly modifying the entire riser, the invention applies local quality changes by creating residual curvature loops at specific locations along the riser length. These loops have different curvature radii tailored to their position, with the first loop having a smaller radius than the second loop, optimizing fatigue resistance locally where compression waves are most severe
2Reliability
If the riser is completely straightened during installation, then dynamic response is reduced, but compression waves and fatigue damage increase at the touch-down point
Solution Approach 1:
The invention converts the potentially harmful effect of residual curvature into a beneficial feature. By intentionally leaving controlled residual curvature loops instead of completely straightening the riser, the loops absorb compression waves and reduce dynamic loads, transforming what would be a defect into a fatigue-protection mechanism
Solution Approach 2:
The invention utilizes curvature by forming loops with specific radius of curvature along the riser. The first loop has a smaller radius of curvature than the second loop, creating a graduated curvature profile that effectively absorbs compression waves and reduces stress concentrations at the touch-down point
3Reliability
If ballast weights are attached to residual curvature loops, then dynamic loads are minimized and fatigue resistance is improved, but installation time and weight increase
Solution Approach 1:
The invention merges the ballast weight attachment with the residual curvature loop formation process. By combining these two functions into a single integrated feature during the straightening process, the installation time increase is minimized while achieving both ballasting and fatigue protection benefits
4Reliability
If multiple residual curvature loops with different radii are formed, then compression wave absorption is optimized, but manufacturing precision requirements increase
Solution Approach 1:
The invention applies parameter changes by varying the curvature radius of successive loops along the riser. The first loop has a smaller radius of curvature than the second loop, creating a graduated parameter profile that optimizes compression wave absorption while the methodology provides guidance for controlling these parameters during installation
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 RCM-installed SCRs provide improved fatigue resistance at a lower cost than alternative solutions, minimizing dynamic loads and reducing compressive waves at the touch-down point, thus extending the riser's lifespan and reducing installation complexity.
Implementation Method 1
SCRs exploit the bending behaviour of rigid pipes in the elastic domain
Implementation Method 2
attaching one or more ballast weights to the at least one loop
Data Source
AI summary
A method of installing a steel catenary riser comprises progressively unspooling and launching the riser into water from a reel-lay vessel. The riser is plastically deformed in a straightening process aboard the vessel, downstream of unspooling and upstream of launching the riser. The straightening process is adjusted to form at least one residual curvature loop of locally increased curvature in a length of the riser that will be suspended in the water above a touch-down point in use. Ballast weights are then attached to the at least one loop. Buoyancy elements may be attached to the riser above the at least one loop.