Double-Walled Conduit Gas Permeation Barrier for Insulation Aging
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Solution Overview
Problem
Existing double-walled line pipes with thermal insulation face issues due to aging of hard foam insulation, particularly polyurethane foam, caused by gas permeation through the plastic outer tube, leading to reduced thermal insulation and mechanical failure at high temperatures.
Innovation Solution
A multi-layer plastic outer pipe with a compact extruded polyethylene terephthalate (PET) gas permeation barrier layer, either as a solid layer or closed-cell foam, is integrated between the inner pipe and the thermal insulation, significantly reducing gas exchange and maintaining insulation properties over the service life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a plastic outer pipe made of polyethylene is used to provide mechanical protection, then the mechanical strength and protection are improved, but gas permeation occurs leading to insulation deterioration
Solution Approach 1:
The outer pipe is constructed as a composite structure with multiple layers: an inner polyethylene layer for mechanical protection, a middle EVOH gas barrier layer to prevent oxygen permeation, and an outer polyethylene layer for additional protection. This composite structure simultaneously achieves mechanical strength and gas impermeability, resolving the contradiction between mechanical protection and insulation reliability.
2Reliability
If a diffusion-regulating layer is placed between the outer pipe and insulation, then gas permeation is reduced, but the layer is damaged during pipe assembly
Solution Approach 1:
The gas barrier function is not uniformly distributed but localized to a specific EVOH layer within the multi-layer pipe structure. This EVOH layer is positioned between two polyethylene layers, giving it local protection while maintaining the overall structural integrity. The barrier function is concentrated where needed without compromising mechanical durability.
Solution Approach 2:
The multi-layer composite structure with EVOH sandwiched between polyethylene layers provides both gas barrier functionality and mechanical durability. The polyethylene outer layers protect the fragile EVOH barrier layer during assembly and service, while the EVOH layer provides the gas permeation barrier function.
3Ease of manufacture
If the outer pipe wall is made thinner to reduce material cost, then manufacturing cost is reduced, but gas permeation increases
Solution Approach 1:
Instead of using a single thick polyethylene wall, the invention uses a multi-layer composite structure with thin layers of polyethylene and EVOH. The total wall thickness is reduced compared to a solid polyethylene pipe of equivalent gas barrier performance, lowering material costs while the EVOH layer ensures low gas permeation.
Solution Approach 2:
The invention changes the material composition parameter by introducing EVOH with its exceptional gas barrier properties. This allows the pipe wall thickness to be reduced while maintaining or improving gas permeation resistance, as EVOH has much lower oxygen permeability than polyethylene.
4Loss of energy
If rigid polyurethane foam is used for thermal insulation, then thermal insulation performance is improved, but oxidation degradation occurs at high temperatures
Solution Approach 1:
The harmful oxygen that causes oxidation degradation of the polyurethane foam is extracted from the system by introducing an EVOH gas barrier layer. This layer actively removes oxygen from reaching the insulation, preventing oxidative degradation and maintaining both thermal insulation performance and mechanical integrity at high temperatures.
Solution Approach 2:
The EVOH gas barrier layer creates an inert environment around the polyurethane foam insulation by blocking oxygen penetration. This protective atmosphere prevents oxidation reactions, allowing the foam to maintain its thermal insulation properties and mechanical strength even at elevated temperatures above 120°C.
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 prevents foam aging, maintains thermal insulation, and ensures mechanical integrity by creating a permeation-tight system, allowing for higher temperatures without reducing the service life of the pipe, while being cost-effective and durable.
Implementation Method 1
a gas permeation barrier layer (7), in particular made of polyethylene terephthalate (PET), as a substantial material component
Implementation Method 2
This oxygen ingress triggers oxidation processes within the insulation... The CO2 bound in the pores diffuses outwards and is replaced by nitrogen from the atmosphere
Implementation Method 3
a thermal insulation layer (4), in particular made of rigid foam, is arranged in an annular gap between the inner pipe and the plastic outer pipe
Implementation Method 4
A multi-layer plastic outer pipe with a compact extruded polyethylene terephthalate (PET) gas permeation barrier layer, either as a solid layer or closed-cell foam, is integrated between the inner pipe and the thermal insulation, significantly reducing gas exchange
Data Source
Figure 1
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AI summary
The invention relates to a double-walled conduit (1) with a medium-carrying inner pipe (2) and a plastic outer pipe (3). A thermal insulation layer (4) made of polyurethane foam is arranged in an annular gap between the inner pipe (2) and the plastic outer pipe (3). The plastic outer pipe (3) is designed as a multi-layer pipe comprising an outer layer (5) of high-density polyethylene (HDPE) with a thickness of approximately 3 mm, an adhesion promoter layer (6) with a thickness of approximately 0.01 mm, and a compactly extruded polyethylene terephthalate (PET) layer as a gas permeation barrier (7) with a material thickness of approximately 1 mm. The polyethylene terephthalate layer forms a highly effective and cost-effective gas permeation barrier (7).