Product Overview

The U-shaped radiant tube—also known as a dual-pass radiant tube—is a mainstream indirect heating device for industrial heat treatment furnaces. The burner and exhaust outlet are positioned on the same side of the furnace wall; flue gas travels along the tube, reverses direction at the U-shaped bend at the far end, and transfers heat to the furnace chamber via infrared radiation from the tube walls.

Radiant tubes isolate the workpiece from flames and combustion flue gases, thereby protecting the furnace’s controlled atmosphere and preventing workpiece oxidation and decarburization. Widely used in various gas-fired heat treatment furnaces, they serve as standard heating elements for continuous annealing furnaces, box-type carburizing furnaces, and car-bottom furnaces.

Working Principle

The gas undergoes complete combustion inside the radiant tube; high-temperature flue gas travels through the first passage to the depths of the furnace, reverses direction via a 180° U-bend, and flows back out through a parallel branch pipe. This recirculating high-temperature flue gas preheats the incoming air, thereby enhancing thermal efficiency; compared to straight radiant tubes, this design effectively reduces the axial temperature gradient along the tube, resulting in a more uniform furnace temperature distribution.

Heat is transferred to the workpiece via thermal radiation through the metal tube walls; the process atmosphere inside the furnace is completely isolated from the combustion system, ensuring the stability of the heat treatment process.

Core Advantages

1.Easy to install and maintain

The burner and exhaust ends are concentrated on the same furnace wall, eliminating the need for openings on both sides and resulting in superior furnace sealing; maintenance and replacement of radiant tubes can be performed without entering the furnace chamber, significantly reducing downtime.

2.Excellent temperature uniformity

The dual-channel, U-turn structure mitigates unidirectional temperature gradients, reduces the temperature differential between the furnace’s high- and low-temperature zones, effectively eliminates heating dead spots, and ensures consistent heat treatment quality across batches of workpieces.

3.Higher thermal efficiency

The recirculating flue gas undergoes continuous heat exchange, fully recovering waste heat; under identical operating conditions, energy consumption is superior to that of traditional straight radiant tubes.

4.Suitable for various atmospheric conditions

Constructed from heat-resistant alloy, the material offers excellent resistance to oxidation, carburization, and sulfur corrosion, making it suitable for complex furnace environments involving nitrogen, endothermic atmospheres, and protective atmospheres.

5.Flexible structure; supports non-standard customization

Pipe diameter, total length, bending radius, and flange connections can all be customized to suit various furnace layouts, including batch furnaces, continuous mesh-belt furnaces, and roller-hearth furnaces.

Selection of Mainstream Materials and Applicable Operating Conditions

Material solutions can be tailored based on the customer’s operating temperature, furnace atmosphere, and start-stop frequency.

1.ZG40Cr25Ni20Si2 (HK alloy)

Long-term operating temperature: ≤1150°C

Features: Manufactured via centrifugal casting, resulting in a dense microstructure; offers creep and carburization resistance. Suitable for carburizing and annealing furnaces; a widely used, mainstream material in the market.

2.310S (0Cr25Ni20) Weldable Grade

Long-term operating temperature: ≤1050°C

Features: Short processing cycle, high cost-performance ratio; suitable for medium-to-low temperature tempering furnaces and bright annealing furnaces.

3.ZG45Ni48Cr28W5Si2

Long-term operating temperature: ≤1250°C

Features: High nickel-chromium alloy offering resistance to high-temperature corrosion and thermal shock; the preferred choice for demanding high-temperature operating conditions involving frequent start-stop cycles.

4.FeCrAl alloy

Suitable for oxidizing atmospheres at medium-to-high temperatures; offers outstanding oxidation resistance and significant cost advantages.

Typical application areas

• Steel Industry: Continuous annealing furnaces for steel strips, hot-dip galvanizing lines, and solution treatment furnaces for steel plates.
• Mechanical Heat Treatment: Gear carburizing furnaces, bogie-hearth quenching furnaces, bearing tempering furnaces, and box-type controlled-atmosphere furnaces.
• Metallurgical Sintering: Powder metallurgy sintering furnaces, ceramic roller kilns
• Non-ferrous metals: Bright heat treatment furnaces for aluminum and copper materials

Key Technical Parameters (Non-standard specifications supported)

• Common outer diameters: Φ80mm–Φ250mm
• Pipe wall thickness: 6–12 mm (cast); 3–6 mm (welded)
• Effective length per unit: ≤4000 mm
• Permissible operating temperature: 800°C–1250°C
• Connection types: Flanged connection or direct plug-in; compatible with various domestic and international burners.

Our Custom Services

1.Provide material selection proposals based on furnace dimensions, furnace chamber temperature, and atmospheric conditions;

2.Customizable U-bend radius, total length, flange dimensions, and mounting brackets;

3.The surface can be coated with a high-temperature radiative coating to enhance radiative heat transfer efficiency;

4.One-stop supply of matching radiant tube supports and sealing assemblies;

5.Direct factory production; supports manufacturing based on drawings and sample prototyping; factory-conducted flaw detection testing is available.

Conclusion

For heat treatment production lines aiming for process stability and reduced operation and maintenance costs, U-shaped radiant tubes have become the preferred heating solution for many furnace manufacturers, thanks to their ease of installation, balanced temperature control, and high reliability.

Whether you are upgrading an existing furnace or building a new heat treatment production line, please provide parameters such as furnace temperature, atmosphere, and chamber dimensions, and we will match you with the most suitable U-shaped radiant tube solution.