Subsea Pipeline End Structure Docking With Passive Heave Damping
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Solution Overview
Problem
The initiation stage of subsea pipeline installation is challenging due to unpredictable movements of the pipelay vessel and pipeline end structure relative to the seabed, leading to potential damage and requiring extended weather windows for installation, especially for small and lightweight pipelines.
Innovation Solution
A method involving a damper, such as a passive heave compensator, is interposed between the pipeline end structure and a subsea anchor to dampen reciprocal motion, allowing accurate docking and laying of the pipeline end structure on the seabed, even in higher sea states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a subsea anchor is pre-installed to provide a fixed point for pipelay vessel, then the vessel can act against bottom tension to initiate laying, but the anchoring process becomes more complex and time-consuming
Solution Approach 1:
A passive heave compensator is introduced as an intermediary device between the pipeline end structure and the subsea anchor. This compensator absorbs relative movements caused by vessel motion and sea states, enabling the pipelay vessel to initiate laying operations even when conditions would normally prevent accurate positioning. The compensator acts as a mediator that decouples the vessel's motion from the docking requirement.
2Measurement precision
If initiation rigging is preinstalled with the anchor to enable connection, then the end structure can be connected to the anchor, but the rigging must be precisely positioned which is difficult due to vessel and end structure movements
Solution Approach 1:
The passive heave compensator is pre-installed on the subsea anchor before the pipelay operation begins. This compensator is designed to accommodate and cushion the unpredictable movements that will occur during the initiation phase. By having the compensator in place beforehand, the system can absorb relative motions between the vessel and seabed, maintaining positioning precision without requiring perfect alignment during the critical docking operation.
3Productivity
If the pipelay vessel operates in higher sea states to extend operational window, then productivity increases, but the end structure experiences larger movements relative to the seabed causing potential damage
Solution Approach 1:
The passive heave compensator serves as a protective intermediary that allows the pipelay vessel to operate in higher sea states without transmitting damaging forces to the pipeline end structure. The compensator absorbs the relative movements and dynamic loads, enabling productivity improvement while protecting the pipeline and end structure from damage that would normally occur in adverse weather conditions.
4Loss of time
If the end structure is lowered quickly to reduce exposure time to weather, then time savings are achieved, but the risk of damage from unpredictable movements increases
Solution Approach 1:
The passive heave compensator is pre-positioned and configured to provide cushioning protection before the end structure is lowered. This allows the end structure to be lowered more quickly with reduced exposure time, while the compensator is already in place to absorb any unpredictable movements or shocks, maintaining reliability despite the faster operation.
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
This approach reduces the need for lengthy weather windows, enabling pipeline installation in adverse conditions and minimizing damage, thus optimizing operational efficiency and cost-effectiveness.
Implementation Method 1
coupling an end structure at a lower end of the element to a subsea anchor via a damper interposed between the element and the anchor; by action of the damper, permitting and damping reciprocal motion of the coupled end structure relative to the anchor
Data Source
AI summary
Subsea laying of an elongate element such as a pipeline is initiated by using a wire to couple an end structure at a lower end of the element to a subsea anchor via a damper interposed between the element and the anchor. Action of the damper allows, but damps, reciprocal motion of the end structure relative to the anchor before and after landing the end structure on a supporting platform defined by parallel rails. In readiness for laying an initial portion of the element on the seabed the end structure is docked to the anchor by moving the end structure along the platform into engagement with a docking formation. The docked end structure then pivots about a horizontal axis in a hinge-over action as the pipeline approaches the seabed.