Subsea Pipe-in-Pipe Laying with Onshore Annulus Degassing
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Solution Overview
Problem
The existing Pipe-in-Pipe pipeline laying methods struggle with achieving optimal thermal insulation due to the lack of time for pressure reduction in the annulus space during pipeline laying, often omitting this step in subsea pipeline installations using the S-lay or J-lay method.
Innovation Solution
A new laying process that involves onshore drying and degassing of the space between the inner and outer pipes, followed by temporary closure with plugs, and a short pumping operation to reduce pressure in the annulus after welding bulkheads, ensuring effective thermal insulation during subsea pipeline installation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If pressure reduction operation is performed to achieve optimal thermal insulation, then thermal insulation performance is improved, but installation time increases due to high degassing times
Solution Approach 1:
The patent applies preliminary action by performing the drying and degassing of the annulus space before the pipeline sections are loaded onto the pipe-laying ship. This allows the time-consuming pressure reduction and degassing operations to be completed onshore in advance, so that when the sections are installed at sea, the thermal insulation is already optimized and no additional time is required for these operations during the actual laying process.
2Productivity
If sections are laid quickly by pipe-laying ship using S-lay or J-lay method, then installation speed is improved, but thermal insulation performance deteriorates due to omission of pressure reduction operation
Solution Approach 1:
The patent applies preliminary action by performing the drying and degassing of the annulus space before the pipeline sections are loaded onto the pipe-laying ship. This allows the time-consuming pressure reduction and degassing operations to be completed onshore in advance, so that when the sections are installed at sea, the thermal insulation is already optimized and no additional time is required for these operations during the actual laying process.
3Reliability
If plugs are used to temporarily close the space between inner pipe and outer pipe, then sealing effectiveness is improved, but device complexity increases
Solution Approach 1:
The patent applies segmentation by dividing the sealing function into two distinct phases: temporary sealing using removable plugs during the drying and degassing operation, and permanent sealing using welded bulkheads during pipeline installation. This segmentation allows each sealing method to be optimized for its specific purpose without compromising the other.
Solution Approach 2:
The patent uses plugs as an intermediary element that temporarily closes the annulus space to enable drying and degassing operations. These plugs serve as a temporary mediator that is later removed and replaced by permanent welded bulkheads, allowing the system to transition from a temporary sealing state to a permanent sealed state.
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 process allows for the installation of subsea pipelines with improved thermal insulation in a reasonable timeframe, maintaining minimal changes to existing laying techniques and enabling the reuse of plugs, while ensuring efficient pressure reduction and insulation.
Implementation Method 1
a short pumping operation to reduce the pressure in the part of the annulus located between this bulkhead and the previously installed bulkhead
Implementation Method 2
drying and degassing the space between the inner pipe and the outer pipe of each section
Implementation Method 3
The fact of positioning insulating material between the two pipes advantageously thermally insulates the inner pipe
Data Source
AI summary
The invention concerns a process and a device for laying a subsea pipeline according to the J-lay or S-lay method wherein straight sections are mounted onshore, dried and degassed then closed by plugs. The sections are loaded on a pipe-laying ship, are separated from their plugs before the welding. At the welding of each bulkhead a short pumping is operated to reduce the pressure in the part of the annulus located between the two last bulkheads and then the opening leading to the annulus are sealed.