Expanded Metal Grid Heating for District Pipe Welding
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Solution Overview
Problem
Existing methods for connecting district heating line sections face challenges such as the risk of short circuits, cold spots, and corrosion due to narrow heating conductors, and require tight tolerances for a reliable welded connection between thermoplastic connecting sleeves and steel pipes.
Innovation Solution
The method involves wrapping strips of expanded metal grid around the ends of jacket pipes, with overlapping sections that are heated using induction coils, allowing for a secure and tight connection without the need for prefabricated conductor rings, and providing transverse slots for enhanced tensile strength and adaptability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If electrically insulated heating conductors are used to heat the joining zone, then the risk of short circuit is reduced, but additional material is introduced that impairs the welded connection
Solution Approach 1:
The harmful insulation material is completely removed from the heating conductor. Instead of using electrically insulated heating conductors, the patent employs an expanded metal grid without insulation, eliminating the source of the problem while maintaining electrical safety through the grid's inherent structure
Solution Approach 2:
The expanded metal grid serves as an intermediary heating element that induces eddy currents through electromagnetic induction. This mediator converts electrical energy to thermal energy without requiring direct electrical contact or insulation, thereby avoiding contamination of the welded joint area
2Temperature
If a strip of expanded metal grid is placed in helical windings around the casing pipe end, then heating effectiveness is improved, but contact lugs must be provided that entail corrosion risk
Solution Approach 1:
The continuous helical winding structure is segmented into discrete strips with overlapping ends. Each strip can be independently installed and secured, eliminating the need for continuous contact lugs that protrude and are exposed to corrosion. The segmentation allows for simpler, more reliable connections without compromising heating effectiveness
Solution Approach 2:
The contact lugs are eliminated by changing the dimensional arrangement from protruding axial elements to planar overlapping strips. The electrical connection is achieved through the overlapping area of the strips themselves, moving the connection interface from a three-dimensional protruding structure to a two-dimensional contact surface that is flush with the pipe surface
3Reliability
If a closed ring made of perforated sheet metal is inserted between the connecting sleeve and pipes, then a tight welded connection is achieved, but narrow tolerances are required that cannot be guaranteed on site
Solution Approach 1:
The material properties are changed from rigid perforated sheet metal to flexible expanded metal grid. This parameter change allows the heating element to deform and adapt to variations in pipe dimensions and alignment, eliminating the need for narrow tolerances while maintaining effective heating and welded connection
4Adaptability or versatility
If strips of expanded metal grid are wrapped around jacket pipes with overlapping sections, then adaptability and ease of installation are improved, but the connection must maintain tightness under mechanical loads
Solution Approach 1:
The strips are pre-formed with overlapping ends designed to interlock. This preliminary preparation ensures that when installed, the strips automatically create a secure, load-resistant connection without requiring additional fastening elements. The overlapping design is pre-engineered to distribute mechanical loads effectively
Solution Approach 2:
The expanded metal grid combines the properties of metal strength with a grid structure that provides flexibility and adaptability. This composite structure maintains tensile strength while allowing the strips to conform to pipe variations and maintain tight connections under mechanical loads
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 ensures a reliable, leak-tight connection that can absorb mechanical loads and maintain tightness, with the expanded metal grid providing a secure, adaptable, and corrosion-resistant interface between the connecting sleeve and the steel pipes, ensuring even heating and extended creepage paths for moisture resistance.
Implementation Method 1
currents are induced in the expanded metal grids closed to form rings via an induction coil placed outside around the connecting sleeve in the area of the joining zones
Implementation Method 2
the thermoplastic material both on the side of the connecting sleeve and on the side of the casing pipes is then melted
Implementation Method 3
use a connecting sleeve in the area of the perforated sheet metal rings enclosing induction coil to induce eddy currents in the perforated metal rings
Implementation Method 4
induce eddy currents in the perforated metal rings, through which the perforated metal sheet is heated
Implementation Method 5
the thermoplastic material both on the side of the connecting sleeve and on the side of the casing pipes is then melted, so that an intimate welded connection between the welding sleeve and the plastic pipes is established
Data Source
Figure 1
Figure 2~3
Figure 4
AI summary
A heat carrier is guided by a steel pipe (2). A tubular casing (3) is equipped with a thermoplastic material for wrapping a heat insulation section (4) and a thermoplastic connecting sleeve (5). Strips (8) and expanded metal interconnect are used as an insert (6) before pushing connecting sleeve onto casing. The ends of casing are welded at sleeve by electrically heating the insert. Welding conditions are set to heat the external induction coils (7) by providing hooked end portions overlapping in circumferential direction, and with connecting sleeve at casing. An independent claim is included for metallic insert for welding thermoplastic jacket tubes of two mutually welded steel tubes of district heating pipe with thermoplastic connecting sleeve.