Induction Welding of Thermoplastic Tubes Without Heating Wires
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Solution Overview
Problem
Existing methods for assembling thermoplastic tubes, particularly in subsea pipelines, face challenges with electro-fusion welding, which can lead to defects and leaks due to heating wires and require lengthy field joint coating processes, and struggle with ensuring corrosion protection in unlined zones.
Innovation Solution
Induction welding using conductive elements to generate a magnetic field, creating a closed-loop or discontinuous welding zone that ensures a precise, reliable, and watertight connection between thermoplastic tubes without the need for heating wires, allowing for remote welding and reduced cooling time.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electro-fusion welding is used to assemble thermoplastic tubes, then the tubes can be connected, but defects and leaks occur due to heating wires
Solution Approach 1:
The patent removes the heating wire component from the welding system entirely. Instead of using electro-fusion welding with heating wires embedded in the tubes, the invention employs induction welding where an external induction coil generates a magnetic field that induces eddy currents in the thermoplastic material itself, eliminating the need for separate heating wires and their associated connectors and defects.
Solution Approach 2:
The patent replaces the mechanical/electrical heating wire system with an electromagnetic induction system. The induction coil generates a time-varying magnetic field that induces eddy currents in the conductive thermoplastic material, converting electromagnetic energy directly into heat within the material being welded, rather than using external heating elements.
2Object-affected harmful factors
If field joint coating is applied to protect unlined zones, then corrosion protection is provided, but the process time increases significantly
Solution Approach 1:
The patent eliminates the field joint coating process entirely by designing the induction welding system to create a watertight seal that inherently protects the weld zone. The induction welding process melts and fuses the thermoplastic material to form a continuous, sealed joint that prevents water ingress and corrosion without requiring additional protective coating layers.
Solution Approach 2:
The induction welding process creates its own protective effect through the welding action itself. The melted thermoplastic material forms a sealed joint that automatically protects the weld zone from corrosion and water ingress, eliminating the need for separate protective coating applications.
3Ease of manufacture
If heating wires are used for electro-fusion welding, then welding can be performed, but the system complexity increases with connectors and wiring
Solution Approach 1:
The patent removes the complex heating wire system including connectors, wiring, and associated components. The induction welding system uses a simple external coil that generates a magnetic field to heat the material without requiring physical contact or electrical connections to the workpiece.
Solution Approach 2:
The patent replaces the mechanical wiring and connector system with an electromagnetic field-based induction heating system. The induction coil can be positioned near the weld zone and generates electromagnetic energy that penetrates the material to create heat internally, eliminating the need for complex electrical connections.
4Reliability
If electro-fusion welding is used, then tube assembly is achieved, but leak paths can form along the heating wire
Solution Approach 1:
The patent eliminates the heating wire that creates potential leak paths. By using induction welding, there is no foreign object (heating wire) embedded in or along the weld zone that could create channels for water or corrosion to travel along.
Solution Approach 2:
The induction welding process creates a seamless fusion of the thermoplastic materials where the melted materials intermix and bond together, forming a homogeneous sealed joint without any embedded objects or interfaces that could create leak paths.
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
This method provides a high-quality, leak-proof weld with reduced risk of failure, optimized operating times, and enhanced corrosion protection, enabling the assembly of thicker tubes and ensuring reliable sealing in subsea environments.
Implementation Method 1
by generating a magnetic field at the level of said welding conductive element(s)
Implementation Method 2
the melting of the thermoplastic materials constituting said contact surfaces by said induction heating of said welding conductive element(s)
Data Source
Figure 1A~2
Figure 3A
Figure 3B
AI summary
The present invention concerns a method for assembling two tubes (1, 2) made from thermoplastic materials, that involves welding by heating two applied rotational contact surfaces of two parts of two tubes (1 ,2), respectively, arranged end to end or overlapping coaxially (XX'). The method involves induction heating of at least one conductive welding element (4), arranged at the interface (3) between the two contact surfaces, by generating a magnetic field at said conductive welding element or elements, such that the melting of the thermoplastic materials constituting said contact surfaces produces a continuous and sealed weld at said interface on at least one closed loop along the entire perimeter of said interface.