Offshore Pipe String Fatigue Management
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The high cost and complexity of installing offshore production riser systems, particularly due to the time-consuming and expensive weld-on pipe couplings used in J-lay methods, which are prone to fatigue failure in deep waters, necessitate a more cost-effective and reliable connection method.
Innovation Solution
The use of high fatigue resistance threaded weld-on couplings in active zones and lower fatigue resistance non weld-on couplings in quiescent zones along the pipe string, reducing the need for expensive weld-on couplings and minimizing fatigue-related damage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If weld-on pipe couplings are used in J-lay pipe strings, then fatigue resistance is improved, but installation cost and time increase significantly
Solution Approach 1:
The patent applies different coupling types in different locations along the pipe string. High-fatigue-resistance weld-on couplings are used only in the upper catenary region where bending stresses occur, while simpler threaded couplings are used in the lower region where pipes rest on the seabed. This local differentiation resolves the contradiction by providing fatigue resistance only where needed, reducing overall installation time and cost while maintaining reliability in critical areas.
2Reliability
If weld-on pipe couplings are used, then fatigue resistance is improved, but manufacturing complexity and cost increase
Solution Approach 1:
The patent differentiates coupling manufacturing complexity by location. Complex weld-on couplings with fatigue-resistant construction are manufactured only for the upper catenary region, while simpler threaded couplings are used elsewhere. This resolves the contradiction by minimizing manufacturing complexity overall while maintaining high fatigue resistance in the specific location where it is required.
Solution Approach 2:
The patent segments the pipe string into different functional zones (upper catenary region subject to bending vs. lower region resting on seabed) and applies different coupling types to each segment. This segmentation allows the system to use complex manufacturing only where necessary, reducing overall device complexity while maintaining reliability where needed.
3Productivity
If threaded couplings are used instead of weld-on couplings, then installation cost and time are reduced, but fatigue resistance decreases
Solution Approach 1:
The patent applies threaded couplings in the lower pipe string region where pipes rest on the seabed and are not subjected to repeated bending stresses. In this location, installation speed is prioritized over fatigue resistance. Meanwhile, weld-on couplings are used in the upper region where fatigue resistance is critical. This local differentiation resolves the contradiction by matching coupling type to the actual stress conditions at each location.
Data Source
AI summary
A pipe string (44) is pulled out by a tug boat (30) from a floating structure (12) such as a production vessel, as pipe sections (54, 56) are connected in series on the vessel, to eventually lay the pipe string in a catenary curve from the vessel to the sea floor and then along the sea floor to a distant subsea well head (86). To save time and cost in coupling the pipe sections, lower fatigue resistant pipe couplings, such as non weld-on couplings (120) that include a threaded sleeve (134), are used to connect pipe sections that will lie in a quiescent zone such as on the sea floor (zone Az), and in a zone (Cz) lying along the middle of the catenary curve. Higher fatigue resistant pipe couplings such as weld-on couplings (150) are used along active zones such as top and bottom zones (Dz, Bz) of the catenary curve.