Flexible Pipe Inner Lining Hydrolysis Protection
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Solution Overview
Problem
Conventional unbonded flexible pipes experience hydrolysis and degradation of polyamide inner linings at elevated temperatures, leading to reduced service life, especially when exposed to crude oil or natural gas.
Innovation Solution
A three-layer inner lining arrangement comprising a fluoropolymer innermost layer, an intermediate olefinic polymer layer, and an outer polyamide layer, with optional adhesion promoters to enhance layer adhesion and stability, reducing hydrolysis and extending the pipe's service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a polyamide inner lining is used to provide good mechanical properties and resistance to hydrocarbons, then the pipe has excellent mechanical strength and chemical resistance, but the polyamide undergoes hydrolysis at elevated temperatures leading to reduced service life
Solution Approach 1:
The inner lining is segmented into three distinct layers with different material compositions: a fluoropolymer layer (innermost), an intermediate layer (polyolefin or polyamide), and an outer polyamide layer. This segmentation allows each layer to perform its specific function - the fluoropolymer provides chemical inertness and resistance to hydrolysis, the intermediate layer provides transition and additional protection, and the outer polyamide layer provides mechanical strength and hydrocarbon resistance.
Solution Approach 2:
The inner lining uses composite material construction by combining fluoropolymer, polyolefin, and polyamide materials in a multi-layer configuration. This composite structure leverages the advantages of each material - fluoropolymer's resistance to hydrolysis and chemical inertness, polyolefin's flexibility and resistance to swelling, and polyamide's mechanical strength and hydrocarbon resistance - while mitigating their individual weaknesses.
2Stability of the object's composition
If polyethylene is used as inner lining material, then the pipe has good flexibility and resistance to swelling, but the nonpolar medium permeates outward through the polyethylene wall to a high degree
Solution Approach 1:
Different layers of the inner lining have different material properties optimized for different functions. The fluoropolymer layer provides excellent gas barrier properties and chemical inertness, the intermediate layer provides resistance to swelling and flexibility, and the outer polyamide layer provides mechanical strength. Each layer's local quality addresses specific requirements rather than using a single material for all functions.
3Temperature
If PVDF is used as inner lining material, then the pipe can operate at temperatures up to 130°C, but blistering and microfoaming occur at temperatures above 130°C due to gas desorption
Solution Approach 1:
The fluoropolymer layer is positioned as the innermost layer in direct contact with the conveyed fluid, providing a barrier that prevents gas desorption and pressure fluctuations from affecting the PVDF or other susceptible layers. This preliminary protective action prevents the blistering and microfoaming issues that occur when PVDF is exposed to high temperatures and pressure changes.
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 three-layer design significantly reduces hydrolysis of the polyamide, thereby prolonging the service life of the unbonded flexible pipe even at elevated temperatures, maintaining integrity and preventing gas desorption.
Implementation Method 1
a) an innermost layer of a fluoropolymer molding composition... The polyamide in the layer according to c) is protected from diffusion of water from the fluid being conveyed by the layer according to a) in a surprising manner, so that hydrolysis of the polyamide is considerably suppressed
Implementation Method 2
The unbonded flexible pipe opposes the diffusion of gases out of a conveyed fluid with a high resistance
Data Source
AI summary
The invention relates to a flexible pipe having a multi-layered structure comprising unbonded layers, comprising an inner lining having the following layer arrangement: a) an innermost layer made of a fluoropolymer molding compound, b) an intermediate layer made of a molding compound on the basis of an olefinic polymer, which is selected from the group consisting of polyethylene, isotactic polypropylene, syndiotactic polypropylene and syndiotactic polystyrene, c) an outer layer made of a polyamide molding compound, wherein the layer made of a polyamide molding compound is particularly efficiently protected against hydrolysis. The pipe is thus particularly suited for offshore applications in oil or gas production.