Flexible Pipe Retaining Layer Radial Expansion Control
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Solution Overview
Problem
Subsea flexible pipes face radial buckling and failure due to extreme depth and dynamic bending loads, which cause swelling of tensile pressure armor layers, leading to irreversible deformation and 'birdcage' shape.
Innovation Solution
A subsea flexible pipe design featuring a retaining layer with polymer fibers having a tensile modulus higher than 55 GPa and elongation at break greater than 4%, wound around tensile pressure armor layers to prevent radial expansion and enhance fatigue resistance, along with a tubular structure and anti-wear layers for protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional reinforcing strips with PPTA homopolymer fibers are used, then the pipe can withstand radial forces and limit swelling, but the pipe fails under extreme depth and dynamic bending loads due to fatigue deterioration
Solution Approach 1:
The invention changes the material parameters of the reinforcing strip by using polyethylene terephthalate (PET) fibers instead of conventional PPTA homopolymer fibers. PET fibers provide a balance between radial strength and fatigue resistance, maintaining the ability to withstand radial forces while significantly improving resistance to deterioration under extreme depth and dynamic bending loads.
Solution Approach 2:
The invention employs composite material construction by combining PET fibers with the existing pipe structure layers. The reinforcing strip made of PET fibers is wound around the tensile pressure armor layers, creating a composite system that leverages the high fatigue resistance and tensile strength of PET while maintaining compatibility with the overall pipe architecture.
2Reliability
If the external sheath is sealed, then hydrostatic pressure opposes swelling of armor layers, but if the external sheath is torn, hydrostatic pressure no longer opposes swelling leading to radial buckling
Solution Approach 1:
The invention applies preliminary anti-action by incorporating reinforcing strips wound around the tensile pressure armor layers before the external sheath is exposed to potential damage. These strips pre-establish resistance against radial swelling, so that even if the external sheath is torn, the armor layers are already constrained and cannot buckle radially inward.
Solution Approach 2:
The reinforcing strip acts as a beforehand cushioning element that is in place before any potential sheath failure occurs. It provides a safety mechanism that cushions against the harmful effect of radial buckling, ensuring that the armor layers remain protected even when the external protective barrier (external sheath) is compromised.
3Strength
If short pitch winding of reinforcing strips is used, then radial swelling is limited, but the pipe becomes heavier and more complex
Solution Approach 1:
The invention optimizes the winding parameters of the reinforcing strip by selecting an appropriate pitch that provides sufficient swelling resistance without excessive weight addition. The short pitch winding is applied with optimized spacing and tension to achieve the minimum necessary reinforcement for swelling control while minimizing material usage and overall pipe weight.
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
The design effectively contains radial expansion, improves fatigue behavior, and maintains mechanical properties at elevated temperatures, preventing 'birdcage' deformation and extending the pipe's operational lifespan under severe conditions.
Implementation Method 1
said polymer fibers further have an elongation at break higher than 4% so that said reinforcing strip is able to undergo deformations without breaking
Data Source
AI summary
A subsea flexible pipe, including an internal sealing sheath (18), at least one tensile pressure armor layer (14, 16) wound around the internal sealing sheath, a retaining layer (12) having at least one reinforcing strip (34), the reinforcing strip having filamentary strands (36) directed substantially longitudinally. The filamentary strands (36) having polymer fibers (38). The polymer fibers have, at room temperature, an elastic modulus in excess of 55 GPa so that the reinforcing strip is able to prevent radial expansion of the armor layer, when the armor layer experiences radial force; and the polymer fibers furthermore have an elongation at break in excess of 4% such that the reinforcing strip is able to undergo deformation without breaking.