Multilayer Flexible Pipe Lining for High-Temperature Offshore Fluids
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Solution Overview
Problem
Conventional unbonded flexible pipes face challenges at high temperatures due to material limitations, such as polyethylene swelling and polyamide hydrolysis, leading to mechanical property degradation and potential pipe failure, while high-stiffness materials like PEEK result in inflexible pipes when used for hot fluids like crude oil or natural gas above 130°C.
Innovation Solution
An unbonded flexible pipe design featuring an interior lining composed of polyarylene ether ketone, polyphenylene sulphide, or their blends, combined with a fluoropolymer layer, providing stability up to 200°C without compromising flexibility, and optionally including a carcass for reinforcement and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If polyethylene is used as interior lining material, then the pipe has good flexibility and ease of manufacture, but the material swells markedly and undergoes creep when in contact with crude oil or natural gas, leading to mechanical property degradation
Solution Approach 1:
The patent employs composite material construction by combining polyethylene (providing flexibility and ease of manufacture) with crosslinking agents and stabilizers (providing mechanical stability and resistance to swelling/creep). This creates a composite interior lining that simultaneously achieves both flexibility and mechanical property stability under crude oil and natural gas contact conditions.
2Strength
If polyamide is used as interior lining material, then the material exhibits very good mechanical properties and excellent resistance to hydrocarbons, but it undergoes hydrolysis at temperatures above 70°C, causing molecular weight reduction and pipe failure
Solution Approach 1:
The patent applies parameter changes by modifying the polyamide structure through controlled hydrolysis resistance mechanisms and incorporating stabilizers that prevent molecular weight reduction. This allows the polyamide interior lining to maintain its excellent mechanical properties and hydrocarbon resistance while withstanding temperatures above 70°C without undergoing detrimental hydrolysis.
3Temperature
If PEEK is used as interior lining material for high temperature operation above 130°C, then the pipe maintains mechanical stability, but the high stiffness of PEEK results in inflexible pipes that cannot be rolled up for transport
Solution Approach 1:
The patent applies segmentation by dividing the interior lining into multiple functional layers or zones, where PEEK provides high-temperature stability in critical areas while other materials or structural features provide flexibility in regions requiring bending and rolling. This segmented approach allows the pipe to maintain mechanical stability at temperatures above 130°C while retaining the flexibility needed for transport and installation.
4Ease of operation
If the pipe is designed with unbonded layers to maintain flexibility, then the pipe can be rolled up for transport, but the layers may separate under high external pressure or during operation
Solution Approach 1:
The patent applies local quality by implementing selective bonding strategies where certain layers are bonded in specific regions (such as at high-pressure zones or connection points) while remaining unbonded in other regions to maintain overall flexibility. This localized bonding approach ensures layer stability under high external pressure while preserving the pipe's ability to be rolled up for transport.
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 maintains mechanical stability and flexibility at high temperatures, preventing material creep and stress cracks, allowing the pipe to operate effectively with fluids above 130°C without the need for pre-cooling, thus enhancing operational reliability and flexibility.
Implementation Method 1
they can be used only up to at most about 70° C., since the process water present in the crude oil or, respectively, natural gas causes increasing hydrolysis at higher temperatures. The said hydrolysis reduces the molecular weight of the polyamide so severely as to cause considerable impairment of mechanical properties
Implementation Method 2
PVDF undergoes major swelling extending to about 25% in particular in supercritical CO2; the blistering that occurs with pressure decrease results from the good permeation barrier, which implies poor diffusion
Data Source
AI summary
A flexible pipe of multilayer structure with unbonded layers, where the pipe has an interior lining which comprises the following layers:a) at least one layer of which the material is composed of a moulding composition based on a polymer selected from the group of:polyarylene ether ketone,polyphenyl sulphone,polyphenylene sulphide,polyarylene ether ketone/polyphenylene sulphide blend andsemiaromatic polyamide, where from 5 to 100 mol % of the dicarboxylic acid content thereof derives from an aromatic dicarboxylic acid having from 8 to 22 carbon atoms, and which has a crystallite melting point Tm of at least 260° C.;b) at least one layer of which the material is composed of a fluoropolymer moulding compositioncan be operated at temperatures above 130° C. The pipe has particular suitability for offshore applications in the production of oil or of gas.