Rigid Rod Load Transfer for Controlled Subsea Splash-Zone Handling
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Solution Overview
Problem
Current methods for lowering and recovering subsea loads, such as wellheads or BOPs, using pipelaying vessels are inefficient due to the need for complex operations and expensive equipment, and pose risks during transit through the splash zone, especially when using pliant load-bearing links like wires or flexible pipes.
Innovation Solution
A method involving a rigid rod supported by a hold-back system on a pipelay tower, where the rod is mechanically coupled to the load and a wire is connected to transfer the load's weight from the hold-back system to the wire once submerged, allowing controlled lowering and recovery through the splash zone without complex equipment or long drill pipes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a crane is used to lift heavy subsea structures, then the lifting capacity is sufficient, but the cost increases greatly and weather restrictions apply
Solution Approach 1:
A rigid rod is introduced as an intermediary component between the hold-back system and the subsea structure. The rod serves as a load-bearing link that transfers forces between the vessel's hold-back system and the heavy structure, enabling the vessel to handle loads beyond its normal crane capacity without requiring a separate heavy-lift crane vessel
Solution Approach 2:
The hold-back system, originally designed for pipeline tensioning, is made multi-functional by enabling it to support and lower heavy subsea structures through the rigid rod mechanism. This allows the pipelaying vessel to perform both pipeline installation and heavy structure deployment using existing equipment
2Ease of operation
If a rigid rod is used to hold the load, then control through the splash zone is improved, but the risk of clash with the hull increases
Solution Approach 1:
The system transitions from using pliant load-bearing links (wires, flexible pipes) to a rigid rod, fundamentally changing the mechanical properties of the load-bearing element. This parameter change provides structural stability and control during splash zone transit, preventing uncontrolled swinging and collision risks associated with flexible elements
3Device complexity
If pliant load-bearing links like wires or flexible pipes are used, then the operation is simpler, but safety during transit through the splash zone is compromised
Solution Approach 1:
The rigid rod acts as an intermediary that bridges the gap between the simplicity of wire-based operations and the safety/control requirements of heavy structure deployment. It provides the structural integrity needed for safe splash zone transit while maintaining a relatively simple operational procedure
Solution Approach 2:
Changing from flexible to rigid load-bearing links fundamentally alters the system's behavior during transit, providing predictable and controlled movement through the splash zone while eliminating the uncontrolled swinging and collision risks associated with flexible elements
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
Enables safe and cost-effective deployment and recovery of heavy subsea structures, reducing weather restrictions and operational complexity, with improved control and safety during the process.
Implementation Method 1
operating the hold-back system to advance the rod downwardly relative to the pipelay tower
Implementation Method 2
the weight of the load is suspended from the hold-back system via the rod
Implementation Method 3
transferring the weight of the load from the hold-back system to the wire
Implementation Method 4
A method involving a rigid rod supported by a hold-back system on a pipelay tower, where the rod is mechanically coupled to the load
Data Source
AI summary
A method of lowering a discrete load from a pipelay vessel comprises holding a rigid rod on an upright launch axis where the rod extends through a hold-back system; coupling a lower end of the rod to the load; connecting a wire to the load either directly or indirectly via the rod; operating the hold-back system to advance the rod downwardly, hence submerging the load, while the weight of the load is suspended from the hold-back system via the rod; when the load is under mater and beneath the splash zone, transferring the weight of the load directly or indirectly from the hold-back system to the wire; and continuing to lower the load in the water, suspended directly or indirectly from the wire. The method may be reversed to recover a load from a subsea location, such as when lifting a wellhead or blowout preventer from the seabed.