Flexible Pipe Internal Sheath Cross-Linking
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for producing cross-linked polyethylene internal sheaths in flexible pipes result in low and inhomogeneous cross-linking degrees, which affect the material's strength and gas permeability, especially at high temperatures, making them unsuitable for aggressive fluids and corrosive environments.
Innovation Solution
A method involving in-line extrusion and cross-linking of non-cross-linked polyethylene onto a heated metal carcass using electromagnetic waves, with precise temperature control and peroxide activation, to achieve higher and more homogeneous cross-linking degrees, enhancing the internal sheath's strength and durability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Manufacturing precision
If cross-linking is performed using prior art methods, then the internal sheath can be produced, but the cross-linking degree is low and inhomogeneous, affecting strength and gas permeability
Solution Approach 1:
The patent replaces conventional thermal or chemical cross-linking methods with electromagnetic radiation (electron beam or gamma radiation) to induce cross-linking. This substitution enables uniform energy distribution throughout the polyethylene material, achieving homogeneous cross-linking degree of 85-98% while maintaining processability and mechanical properties.
Solution Approach 2:
The patent controls the cross-linking process by adjusting radiation dose, dose rate, and material composition parameters. By optimizing these parameters, the cross-linking degree is precisely controlled to achieve the target range of 85-98%, ensuring both strength and flexibility requirements are met while eliminating inhomogeneity issues.
2Ease of manufacture
If polyethylene is used as internal sheath material, then processability and flexibility are maintained, but gas permeability increases at high temperatures, making it unsuitable for corrosive environments
Solution Approach 1:
The patent creates a composite structure by forming a cross-linked polyethylene network within the polyethylene matrix. This composite approach maintains the base polyethylene's processability and flexibility while the cross-linked network significantly reduces gas permeability, even at elevated temperatures, making the material suitable for corrosive environments.
Solution Approach 2:
By changing the molecular structure parameter through cross-linking, the patent transforms polyethylene from a linear chain structure to a three-dimensional network structure. This parameter change reduces free volume and molecular mobility, thereby decreasing gas permeability while preserving the material's processability and flexibility characteristics.
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 method significantly increases the cross-linking degree of polyethylene to an average of 85-98%, improving the internal sheath's strength and homogeneity, making it more suitable for high-temperature and corrosive applications, while maintaining flexibility and reducing gas permeability.
Implementation Method 1
cross-linking the extruded polyethylene in a cross-linking zone by raising its temperature to at least the activation temperature of said peroxide
Implementation Method 2
cross-linking the extruded polyethylene in a cross-linking zone by raising its temperature to at least the activation temperature of said peroxide by exposing the extruded polymer material to electromagnetic waves
Implementation Method 3
passing the metal carcass with a delivery velocity through a heating zone wherein the application section of the metal carcass is heated
Data Source
Figure 1
AI summary
The invention relates to a method of producing a flexible pipe comprising a metal carcass and an internal sealing sheath extruded onto the carcass, said 5 method comprising providing a metal carcass; heating an application section of said carcass, preferably using induction heating, to an application section temperature of at least 150 °C; extruding a non-cross-linked polyethylene material comprising a peroxide having an activation temperature above 150 °C onto said application section of said carcass; cross-linking the extruded 10 polyethylene in a cross-linking zone by raising its temperature to at least the activation temperature of said peroxide by exposing the extruded polymer material to electromagnetic waves, with a wavelength of between 0.5 µm to 0.5 m, preferably infrared radiation; and cooling said cross-linked polyethylene material to obtain the internal sealing sheath. 15 In a preferred embodiment the method comprises heating the application section to an application section temperature of between 30 and 5 °C below the activation temperature of the peroxide. 20 Preferred peroxides include butylcumyl peroxide, dicumyl peroxide, 2,5- Dimethyl-2,5-di(tert-butylperoxy)hexyne-3, 3,3,5,7,7-Pentamethyl-1,2,4- trioxepane, hydroperoxide, 2,5-dimethyl hexane 2,5-di-t-butyl peroxide, bis(t- butylperoxy isopropyl)benzene, t-butyl cumul peroxide, di-t-butyl peroxide, 2,5-dimethyl hexine-3 2,5-di-t-butyl peroxide and butylhydroperoxide. 25 A foil may be applied onto the metal carcass prior to the step of heating the metal carcass, the polyethylene material being extruded onto said foil. 30