Induction Welding of Thermoplastic Tubes for Leakproof Joints
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Solution Overview
Problem
Existing methods for assembling thermoplastic tubes, particularly undersea pipes, face challenges such as leakage risks due to electrofusion welding and the time-consuming process of field joint coating, which can lead to fragile welds and corrosion issues.
Innovation Solution
The method employs induction welding using conductive welding elements made of metal, such as steel, to create a leakproof and reliable connection between thermoplastic tubes by generating a magnetic field with an electromagnetic induction coil, ensuring a continuous weld around the perimeter without the need for heater wires or direct electrical contact.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If electrofusion welding is used to assemble thermoplastic tubes, then the welding process can be performed with direct electrical contact, but leakage risks increase and weld reliability decreases
Solution Approach 1:
The patent replaces the electrofusion welding system (which uses electrical heating elements embedded in the weld joint) with an induction welding system that uses electromagnetic fields to heat conductive welding elements. This substitution eliminates the need for direct electrical contact and embedded heater wires, thereby removing leakage paths while achieving reliable welds through induction heating of metal welding elements that melt the thermoplastic material.
Solution Approach 2:
The patent introduces conductive welding elements (such as metal rings or wires) as intermediaries in the welding process. These elements are positioned at the weld interface and heated by induction, serving as a mediator that transfers thermal energy to melt the thermoplastic material without requiring direct electrical contact between the power source and the joint, thus eliminating leakage risks while maintaining weld integrity.
2Object-affected harmful factors
If field joint coating is performed to protect non-lined zones, then corrosion protection is provided, but the process becomes time-consuming and complex
Solution Approach 1:
The patent extracts the need for field joint coating by extending the thermoplastic liner continuously through the weld joint and melting it during the welding process. This eliminates the non-lined zone that would otherwise require separate corrosion protection coating, thereby removing the time-consuming coating application step while maintaining corrosion protection through the integrated liner design.
Solution Approach 2:
The patent merges the liner protection function with the welding process itself. By extending the liner through the joint and using the welding heat to melt and seal the liner material, the corrosion protection function is combined with the joining operation, eliminating the need for separate coating application and reducing overall process time.
3Reliability
If induction welding with conductive elements is used, then weld strength and leakproofing are improved, but the device complexity increases due to electromagnetic induction coil
Solution Approach 1:
The patent discards the complex electrofusion heating elements and electrical connection systems, replacing them with a simpler induction heating system. The electromagnetic induction coil generates magnetic fields that induce eddy currents in the conductive welding elements, which self-heat through resistive heating. This approach eliminates the need for complex electrical connections and embedded heaters, reducing overall equipment complexity while achieving reliable, leakproof welds.
4Strength
If thicker thermoplastic tubes are welded, then structural integrity is maintained, but cooling time increases significantly
Solution Approach 1:
The patent applies local quality by concentrating the heating action precisely at the weld interface through induction heating of conductive elements positioned at the joint. This localized heating melts only the necessary amount of thermoplastic material at the interface without excessively heating the entire tube wall. Consequently, even thicker tubes can be welded while maintaining structural integrity, and the focused heating reduces overall cooling time because only the weld zone requires cooling rather than the entire tube assembly.
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 approach results in a stronger, more reliable weld with reduced risk of leakage and faster cooling times compared to electrofusion welding, allowing for efficient assembly of thermoplastic tubes, including those with thinner sections, while ensuring complete leakproofing and minimizing corrosion risks.
Implementation Method 1
an electromagnetic field is generated at said interface (3) using an electromagnetic induction coil (5) arranged coaxially inside the two tubes
Implementation Method 2
heated by induction by generating a magnetic field at said conductive welding element(s) so that the melting of the thermoplastic materials
Data Source
AI summary
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.