Trace-Heated PiP Transition Section for Reel-Lay Pressure Isolation
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Solution Overview
Problem
The challenge lies in efficiently spooling and installing electrically trace-heated subsea pipe-in-pipe (PiP) pipelines end-to-end onto a reel, particularly in maintaining the integrity of heating elements and low pressure within the annulus, while avoiding the need for repeated drawdown operations and ensuring electrical continuity during reel-lay operations.
Innovation Solution
A transition section is introduced, comprising an inner and outer pipe with an annulus containing heating cables and inflatable seals that allow fluid communication and isolation, enabling continuous monitoring and maintaining low pressure, allowing for seamless spooling and separation of pipelines without re-pumping, and ensuring electrical continuity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If multiple PiP pipelines are spooled successively onto the same reel, then installation efficiency is improved, but maintaining low pressure in the annulus and electrical integrity of heating elements becomes more difficult
Solution Approach 1:
The transition section divides the annulus into separate sealed zones using inflatable seals that can isolate each pipeline section. This segmentation allows each zone to maintain its low pressure independently while enabling successful spooling of multiple pipelines onto the same reel.
Solution Approach 2:
The transition section acts as an intermediary component between two PiP pipeline sections, providing the necessary sealing and pressure isolation functionality that enables multiple pipelines to be spooled together without compromising their individual pressure integrity or heating element electrical continuity.
2Ease of operation
If pipelines are spooled with bending beyond elastic limits, then spooling capability is improved, but plastic deformation and ovalisation increase
Solution Approach 1:
The transition section incorporates flexible design elements and appropriate material selection that allow the pipe to accommodate bending beyond elastic limits during spooling while minimizing permanent plastic deformation and maintaining acceptable ovalisation levels within the annulus.
3Temperature
If heating elements are installed in the annulus, then thermal management is improved, but risk of crushing heating elements during spooling increases
Solution Approach 1:
The transition section is designed with adequate annulus width and appropriate spacing between the inner and outer pipes to provide a cushioning effect that protects heating elements from crushing during spooling operations, while still allowing effective thermal management functionality.
4Reliability
If drawdown operations are performed separately on each pipeline, then pressure control is improved, but time consumption increases
Solution Approach 1:
The transition section enables drawdown operations to be performed on multiple pipeline sections simultaneously by providing a common access point and interconnected sealed zones, thereby reducing total operation time while maintaining proper pressure control in each section.
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 solution allows for efficient spooling and installation of electrically trace-heated PiP pipelines by maintaining low pressure and electrical integrity, reducing the need for repeated drawdown operations and ensuring continuous monitoring, thereby streamlining the reel-lay process and preventing pipeline disruptions.
Implementation Method 1
heat may be added by electrical heating systems that comprise elongate heating elements such as wires
Implementation Method 2
an annulus containing heating cables that extend longitudinally between annuli of the pipelines and also containing longitudinally-spaced seals that are switchable between a deactivated state to effect fluid communication between the annuli of the pipelines and an activated state to isolate the annuli of the pipelines from each other
Data Source
Figure 1~2
Figure 3~5
Figure 6~7b
AI summary
A transition section (10) disposed between successively-spoolable electrically trace-heated PiP pipelines (12) comprises an inner pipe, an outer pipe and an annulus between the inner and outer pipes. The annulus contains heating cables (26) that extend longitudinally between annuli of the pipelines and longitudinally-spaced seals (44) that, when deactivated, allow fluid communication between the annuli of the pipelines and, when activated, isolate the annuli of the pipelines from each other. Longitudinally-spaced blocking plates (32) close the lumen of the inner pipe and define an inner chamber between them. Longitudinally-spaced openings (40) penetrate a wall of the inner pipe at locations longitudinally inboard of the blocking plates and the seals. The openings effect fluid communication between the annulus and the inner chamber and also define a diversion path for the heating cables that extends from the annulus to the inner chamber and back to the annulus.