Flexible Pipe Polymer Layer Strain Localization
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Solution Overview
Problem
Flexible pipes used in deep and ultra-deep water environments face challenges due to extreme pressure and temperature, leading to localized strain and microcrazing in polymer layers, which can result in pipe failure and reduced lifespan.
Innovation Solution
A method of producing flexible pipes with a tubular layer formed by coextruding an inner sub-layer with a lower modulus of elasticity than the outer sub-layer, directly chemically bonding them, and forming an armour layer with gaps, to reduce strain localization and microcrazing, using materials like PVDF, HDPE, and PEEK.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If a polymer layer is used in flexible pipes for deep water applications, then the pipe can transport production fluids in extreme environments, but the polymer layer is subjected to severe localized strain and tends to creep into gaps of armour layer, leading to microcrazing and reduced pipe lifetime
Solution Approach 1:
The patent applies parameter changes by modifying the molecular weight distribution of the polymer material. Specifically, it uses a bimodal or multimodal polymer composition with both high molecular weight (for strength and creep resistance) and low molecular weight (for flexibility and strain distribution) components. This changes the material parameters to simultaneously achieve adaptability to extreme environments and maintain layer integrity under localized strain.
Solution Approach 2:
The patent employs composite materials by combining polymer layers with armour layers in a multi-layered flexible pipe structure. The composite design integrates materials with different properties: the polymer layer provides flexibility and corrosion resistance, while the armour layer provides mechanical strength. The interface between these composite layers is engineered to prevent harmful interactions while maximizing overall performance in deep water environments.
2Power
If internal pressure is applied to the pipe at high pressures (about 8000 psi / 55 MPa or more), then the pipe can transport production fluids, but the strain distribution within the polymer layer becomes highly localised at the areas around the gaps, resulting in microcrazing or microcracking
Solution Approach 1:
The patent changes the material parameters by using polymers with specific molecular weight distributions (bimodal or multimodal) that enable the material to distribute strain more uniformly under high internal pressure. The low molecular weight component allows the polymer to deform more uniformly, preventing highly localized strain concentration around armour layer gaps that would otherwise lead to microcrazing.
3Ease of operation
If the polymer layer deforms and creeps into the gaps of armour layer under pressure, then the pipe maintains flexibility, but this deformation leads to cavitation rather than plastic flow and formation of microcrazing on the radially inner surface
Solution Approach 1:
The patent modifies material parameters by using a bimodal or multimodal polymer composition where the low molecular weight component provides enhanced flexibility and deformability. This allows the polymer layer to creep into armour layer gaps without causing cavitation, as the material can flow more uniformly rather than forming voids. The high molecular weight component maintains sufficient strength to prevent microcrazing formation.
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 solution effectively reduces the occurrence of strain localization and microcrazing, enhancing the pipe's resistance to pressure and temperature extremes, thereby extending its operational life and preventing pressure containment loss.
Implementation Method 1
directly chemically bonding the inner sub-layer to the outer sub-layer
Implementation Method 2
the armour layer is usually formed from interlocking wires of certain cross section, and there are certain gaps between adjacent windings. The polymer layer tends to deform and creep into the gaps when under pressure.
Implementation Method 3
producing a tubular layer by coextruding an inner sub-layer (304) and an outer sub-layer (302)
Data Source
Figure 1
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AI summary
A flexible pipe body layer and method of producing a flexible pipe body layer are disclosed. The method includes coextruding an inner sub-layer and an outer sub-layer, wherein the inner sub-layer and outer sub-layer comprise a polymer, and wherein the inner sub-layer has a lower modulus of elasticity than the outer sub-layer.