Subsea Pipe-in-Pipe Annulus Projections for Thermal Buckling
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Solution Overview
Problem
Subsea pipelines, particularly those with a pipe-in-pipe configuration, face challenges in mitigating buckling due to thermal expansion and frictional forces, which can lead to costly interruptions and damage, especially when buried or anchored.
Innovation Solution
The pipeline design includes longitudinally-spaced outward and inward projections that allow the inner pipe to move relative to the outer pipe, limiting thermal expansion and reducing frictional resistance, thereby controlling buckling without the need for bulkheads or complex interface formations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If the pipeline is anchored or buried to prevent upheaval buckling, then outer pipe stability is improved, but inner pipe buckling susceptibility increases due to restricted longitudinal movement
Solution Approach 1:
The pipeline is divided into modular sections with discrete interlocking projections at intervals. These segmented connections allow the inner pipe to move independently within each section while maintaining overall structural stability, resolving the conflict between outer pipe anchoring and inner pipe buckling prevention.
Solution Approach 2:
The inner pipe is nested within the outer pipe, with interlocking projections extending into the annulus. This nested configuration allows the inner pipe to maintain longitudinal movement capability while being protected by the outer pipe structure, addressing both stability and buckling resistance requirements.
2Reliability
If conventional steel bulkheads are used to lock the inner pipe against longitudinal movement, then buckling is mitigated, but thermal insulation performance deteriorates due to thermal bridging
Solution Approach 1:
The interlocking projections are made from thermally-insulating material that forms a composite structure with the inner and outer pipes. This composite approach provides buckling mitigation through mechanical interlocking while maintaining thermal insulation performance by using materials with low thermal conductivity, eliminating the thermal bridging problem of steel bulkheads.
3Reliability
If the inner pipe is fully restrained to prevent thermal expansion, then buckling is controlled, but compressive forces increase leading to potential failure
Solution Approach 1:
The interlocking projections provide dynamic restraint rather than fixed constraint. The inner pipe can move longitudinally within the annulus until the projections engage, at which point buckling is controlled. This dynamic system allows thermal expansion to occur naturally while providing restraint only when needed, minimizing compressive forces.
4Reliability
If complex interface formations or bulkheads are added to mitigate buckling, then buckling control is improved, but device complexity increases
Solution Approach 1:
The interlocking projections serve multiple functions simultaneously: they provide buckling mitigation through mechanical interlocking, maintain thermal insulation by using insulating materials, allow controlled longitudinal movement, and simplify the overall structure by eliminating the need for separate bulkheads or complex interface formations. This multi-functionality reduces device complexity while improving reliability.
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 design reduces compressive forces on the inner pipe, allowing for thermal expansion without significant frictional resistance, thereby preventing buckling and maintaining pipeline integrity while minimizing thermal insulation reduction.
Implementation Method 1
resistance to thermal elongation due to friction and cohesion between the exterior of the pipeline and the seabed soil results in axial compressive forces
Implementation Method 2
a pipeline that is subjected to an increase in temperature will tend to extend longitudinally
Data Source
Figure 1a~1c
Figure 2~3
Figure 4~5
AI summary
A subsea pipeline (10) of pipe-in-pipe configuration comprises an inner pipe (14), an outer pipe (16) spaced radially from the inner pipe and an annulus (20) defined by the radial spacing between the inner and outer pipes. A series of longitudinally-spaced outward projections (22) extend radially outwardly into the annulus from the inner pipe and are movable longitudinally relative to the outer pipe. A corresponding series of longitudinally-spaced inward projections (24) extend radially inwardly into the annulus from the outer pipe and are movable longitudinally relative to the inner pipe. When the inner pipe is subject to thermal elongation or contraction in use of the pipeline, the inner pipe is movable longitudinally relative to the outer pipe, hence moving the outward projections between and relative to the inward projections. The pipeline may be buried to restrain the outer pipe. The annulus may be flooded, in which case the inner pipe is covered with wet insulation.