Spiral Wrapped Fin Tube
L, LL/KL Fin Tubes
- Fin Tube Types: L, LL, KL.
- Manufacturing Process: The fins are wrapped onto the outer surface of the base tubes in different ways.
- Base Tube Material: Carbon steel, alloy steel, stainless steel, duplex steel, copper tube.
- Fins: Aluminum 1060, Aluminum 1100, T2 copper
- Applications: Air coolers, heat exchangers, air heaters, economizers
L/LL/KL Fin Tube Technical Specifications
What AGICO Supplies
AGICO supplies a series of L-foot fin tubes, including L, LL and KL finned tubes for customers in many industries. Here is the specification table. Customers can have detailed customization of the dimensions and materials of fin tubes. If you need a free quote, check the details and make your order now.
L/LL/KL Fin Tube Size and Materials
| Parameter | Specification / Range |
|---|---|
| Base Tube Outer Diameter (OD) | 16mm ~ 51mm (up to 219mm available) |
| Base Tube Wall Thickness | 1mm ~ 8mm (varies with OD) |
| Fin Height | 7mm ~ 16mm (up to 20mm optional) |
| Fin Thickness | 0.28mm ~ 0.8mm (commonly 0.3mm ~ 0.6mm) |
| Fin Pitch (spacing) | 2.3mm ~ 6mm |
| Tube Length | Up to 21,000mm (subject to manufacturing) |
| Base Tube Materials | Carbon steel, Stainless steel, Alloy steel, Copper, Titanium |
| Fin Materials | Aluminum (1060, 1070, 1100), Copper |
Wrapped Type- L, LL, and KL Fin Tubes Introduction
- L Type Fin Tube: Wrapped Fin Tube
- LL Finned Tube: Overlapped Wrapped Fin Tube
- KL Finned Tube: Knurled Wrapped Fin Tube
L-foot fin tubes refer to 3 types of fin tubes featuring L-shaped fins—L, LL and KL fin tubes. These 3 types of fin tubes are also known as wrapped fin tubes, or spiral wound fin tubes.
They are manufactured in the following process:
first, an aluminum (or copper) strip is formed into an L-shaped foot, then wound around the base tube under tension, with the fin foot wrapping tightly against the tube wall. They are the most common fin tubes in the fabrication of various types of heat exchangers.
L-type Fin Tube
For L type fin tube fabrication, the trapezoidal cross-section of the L-type fin is formed through a rolling process; these fins aligns with the heat flux density distribution. The tight bond between the fin and the tube ensures high thermal efficiency and eliminates the contact thermal resistance often caused by unavoidable gaps in “sleeve-on” (or stacked-plate) finned tubes.
- Max Working Temperature: 230°C
- Features: L type fin tubes are produced via a winding process, offering high production efficiency, uniform fin spacing, excellent heat transfer performance, and a high fin-to-tube area ratio; with fins covering the base tube, it is protected against atmospheric corrosion.
- Applications: Primarily used for air coolers and air heaters in industries such as petrochemicals, power generation, papermaking, tobacco, and building heating, as well as for air heaters in spray-drying systems for products like plant protein powder and starch in the food industry.
LL-type Fin Tube
LL-type finned tubes is developed based on the L-type design—the fin base covers the outer surface of the base tube, thereby reinforcing the contact interface and enhancing heat transfer efficiency. Its fin strip is pre-formed into a stepped double-L foot and helically wound under tension; the foot of the subsequent fin wrap overlaps that of the preceding one, ensuring a more complete and continuous coverage of the base tube surface.
- Max Working Temperature: 180°C
- Dimensions: Base tube outer diameter: 12.7–50.8 mm; tube length: 300–20,000 mm; fin height: 6.35–25.4 mm; 5–12 FPI; strip thickness: 0.30–0.50 mm.
- Applications: It is a cost-effective fin tube option for low-temperature, corrosive atmospheric environments.
KL-type Fin Tube
KL-type finned tubes, also known as knurled finned tubes, are produced by knurling the base tube prior to fin winding or by using a winding machine equipped with a knurling tool alongside the winding blade; the knurling and winding processes occur simultaneously.
Working Condition: maximum operating temperature: ≤250°C; maximum operating pressure: ≤3.2 MPa
Features:
- High heat transfer performance and low contact thermal resistance.
- Large contact area between the fin and the tube, ensuring a tight and secure fit.
- Good resistance to atmospheric corrosion and stable long-term performance.
Why Choose L, LL, KL-type Fin Tubes from AGICO
- Large heat transfer area: 4–8 times that of plain tubes, offering high cooling/heating efficiency.
- Compact structure: Smaller volume for the same heat transfer capacity, saving space.
- Low cost: Mature cold-winding process and affordable pricing make it suitable for mass application.
- Flexible Material Options: Carbon steel (economical), stainless steel (corrosion-resistant), and aluminum (lightweight, good thermal conductivity).
Quality Control
AGICO has quality control at each step of L-foot-type fin tube manufacturing, including raw material inspection, groove dimensional inspection, fin tightness inspection, hydrostatic test, eddy current test, etc.
L/LL/KL Finned Tubes Manufacturing Process
L/LL and KL finned tubes and G-type finned tubes belong to the spiral wound fin tube type, while G-type finned tubes are the embedded type. L/LL and Kl finned tubes are wrapped fin tubes; their manufacturing methods are slightly different:
- L-type and LL-type Finned Tubes: The manufacturing process adopts state-of-the-art CNC L-type finning machines; these tubes utilize digital control to maintain optimal bonding between the tube and the fin. The trapezoidal cross-section—formed through a rolling process—aligns with the heat flux density distribution; this design saves material while significantly enhancing thermal efficiency and eliminating the contact thermal resistance inherent in “sleeve-on” (or “slide-on”) finned tubes, where gaps between the tube and fin cannot be fully removed.
- KL-type Finned Tubes: The KL-type finned tube requires a knurled base tube; after the fin is wound on, the root of the L-shaped aluminum fin undergoes a secondary rolling process to strengthen the bond. This unique process increases the contact area by approximately 50%, minimizes contact thermal resistance, and delivers high heat transfer performance, ensuring the assembly remains secure even under repeated thermal cycling.
L, LL and KL Fin Tube Property Comparison
Comprehensive Comparison • Bonding • Corrosion • Temperature • Cost
| Feature | L Fin | LL Fin | KL Fin |
|---|---|---|---|
| Bonding | Wrapped (base tube wrapped) | Tight‑wrapped (improved contact) | Embedded (mechanical interlock) |
| Corrosion Resistance | Fair (gaps allow moisture) | Good (tighter wrap reduces crevices) | Excellent (no gaps, fully protected) |
| Temperature Range | Up to 250 °C | Up to 350 °C | Up to 450 °C |
| Cost | Low (most economical) | Medium (balanced performance) | High (premium investment) |
– L • LL • KL — Choose based on operating environment & budget
FAQ of L-foot Wrapped Type Fin Tubes
Yes, the “L-foot” finned tube is a type of wrapped finned tube. It is manufactured by spirally winding a metal fin strip under tension around the exterior of a base tube,it is also known as a spirally wrapped finned tube.
There are many options for the base tube material; common materials include carbon steel, stainless steel, alloy steel, copper, titanium, and nickel. Fin materials are primarily aluminum and copper.
Max temperature ratings are: L-type (150°C), LL-type (180°C), and KL-type (260°C). For high-temperature applications exceeding 260°C, the G-type (embedded) finned tube is a more suitable choice.
Yes. Many manufacturers offer customization services; the fin pitch can be adjusted according to customer requirements, typically ranging from 2.1 mm to 6.0 mm.
It depends on the specific operating conditions:
G-type (Embedded): Suitable for high-temperature applications (e.g., charge air coolers, process gas heaters); offers low thermal contact resistance and high long-term thermal efficiency.
L-type (Wrapped): Suitable for general industrial services, HVAC, and scenarios where cost-effectiveness and moderate temperatures are priorities. KL-type (Overlapped): Suitable for highly corrosive environments (e.g., air coolers in coastal areas or chemical plants); the fin fully covers the base tube, providing excellent corrosion protection.
Choose G-type for high temperatures and requirements for stable long-term thermal efficiency; choose L-foot for moderate temperatures and cost-sensitive applications; consider LL or KL types for highly corrosive environments.
Finned tubes typically adhere to the following international standards:
ASME: Covers specifications for the design, manufacturing, and inspection of pressure vessels and heat exchangers.
ASTM: Specifies the chemical composition, mechanical properties, and corrosion resistance of base tube and fin materials.
Specific material standards include: ASTM A179/ASME SA179 (cold-drawn low-carbon steel seamless tubes for heat exchangers), ASTM A213/ASME SA213 (stainless steel tubes), etc.
Regional standards such as DIN, EN, and JIS are also available options.
