Steel Catenary Riser Ballasted Curvature Loops for Touch-Down Fatigue
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Conventional steel catenary risers (SCRs) experience fatigue-induced failure due to repetitive motion from floating upper supports and sea conditions, leading to potential rupture, especially in deep or ultradeep waters, without viable cost-effective alternatives that maintain the advantages of rigid pipe systems.
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 flexibility and fatigue resistance by absorbing dynamic loads, while maintaining a rigid structure.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional rigid steel pipes are used in SCR, then structural strength and cost-effectiveness are improved, but fatigue resistance deteriorates due to repetitive motion at the touch-down point
Solution Approach 1:
The patent applies local quality by creating a touch-down portion with different properties from the rest of the riser. Specifically, the pipe wall thickness is increased in the touch-down portion (from typical 9-12mm to 15-25mm or more), and residual curvature is introduced only in this localized region. This local modification enhances fatigue resistance where needed without compromising the overall structural strength or requiring complete replacement of the rigid pipe system.
Solution Approach 2:
The patent introduces dynamics by creating a flexible touch-down portion through residual curvature within the rigid pipe structure. The residual curvature allows the touch-down portion to bend and absorb dynamic loads from repetitive motion, while the rest of the riser maintains its rigid characteristics. This dynamic capability is achieved while keeping the pipe material and overall structure fundamentally rigid, resolving the contradiction between rigidity and fatigue resistance.
2Reliability
If the pipe wall thickness is increased to improve fatigue resistance, then structural strength is improved, but weight and installation complexity increase
Solution Approach 1:
The patent applies local quality by concentrating the increased pipe wall thickness specifically in the touch-down portion where fatigue occurs, rather than increasing thickness along the entire riser length. The touch-down portion may have 15-25mm or more thickness, while other portions maintain typical 9-12mm thickness. This localized approach improves fatigue resistance while minimizing overall weight increase.
Solution Approach 2:
The patent segments the riser into distinct portions with different properties: a rigid upper portion, a flexible touch-down portion with increased thickness and residual curvature, and a rigid lower portion. This segmentation allows each section to be optimized for its specific function, with the touch-down portion bearing the brunt of fatigue loads through its enhanced properties.
3Reliability
If residual curvature is introduced to reduce dynamic loads, then fatigue resistance is improved, but manufacturing complexity increases
Solution Approach 1:
The patent applies preliminary action by introducing residual curvature into the pipe during the manufacturing or pre-installation phase, before the riser is deployed. This pre-formed residual curvature is then activated during installation when the riser is laid on the seabed, creating the flexible touch-down portion. This preliminary preparation simplifies the overall installation process compared to attempting to create residual curvature in-situ.
Solution Approach 2:
The patent applies parameter changes by modifying the geometric parameters of the pipe in the touch-down portion - specifically introducing residual curvature (a curvature parameter) and increasing wall thickness. These parameter changes transform the rigid pipe into a flexible section capable of absorbing dynamic loads, while the modification methods (such as thermal or mechanical forming) are integrated into existing manufacturing capabilities.
4Reliability
If flexible pipes are used instead of rigid pipes, then fatigue resistance is improved, but structural strength and cost-effectiveness deteriorate
Solution Approach 1:
The patent applies local quality by creating a flexible touch-down portion only where needed (at the seabed contact point), while the majority of the riser maintains its rigid pipe construction. The flexible portion is achieved through residual curvature and increased wall thickness in a localized region, allowing the rigid pipe to retain its overall structural strength and cost advantages while gaining fatigue resistance where required.
Solution Approach 2:
The patent segments the riser into rigid and flexible portions, with the flexible touch-down portion serving as a transition zone between the rigid pipe and the seabed. This segmentation allows the system to combine the advantages of both rigid and flexible pipes: the rigid portions provide structural strength and cost-effectiveness, while the flexible portion provides fatigue resistance.
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 method significantly reduces fatigue-induced damage and dynamic loads at the touch-down point, extending the riser's life and maintaining cost-effectiveness compared to complex flexible or buoyancy-based solutions.
Implementation Method 1
attaching one or more ballast weights to the at least one loop
Implementation Method 2
The method significantly reduces fatigue-induced damage and dynamic loads at the touch-down point
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
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.