The different types of finned tubes


Finned tubes are used to cool or heat fluids or to recover waste heat. On the air side of the tube, the surface is enhanced by fins which are designed to increase the surface area of the tube and improve thermal performance.

There are many different types of finned tubes on the market today. Use the guide below to help find the right one for your application.

Helical high fins

Helical high finned tubes are used to repair air-cooled heat exchangers and are available in 5 variations:

  • ‘L’ finned tubes

The ‘L’ fin is one of the most common types of finned tube. It relies on maximum surface contact between the fin and tube.

Supplied in ductile metals, such as aluminium and copper, ‘L’ fin tubes withstand temperatures between 150-170°C, as well as compression, and allow for stretching during installation.

  • ‘LL’ finned tubes

‘LL’ finned tubes have overlapping feet which enclose the base of the tube. The overlapping fin prevents movement and separation and protects the entire tube against corrosion.

In corrosive environments, ‘LL’ fins are an excellent alternative to expensive extruded fins.

  • ‘KL’ finned tubes

‘KL’ finned tubes have fins which are made from a strip of metal that’s machined into an accurately controlled L-shaped foot. The fin is then rolled into the pre knurled tube and secured at each end.

The ‘KL’ finned tube provides a tight bond which enhances heat transfer and withstands temperatures up to 250°C.

  • ‘G’ embedded finned tubes

An embedded heat exchanger tube is designed to be durable and is suitable for high temperatures or applications where the fin side will be subject to regular cleaning.

Some ‘G’ embedded finned tubes incorporate carbon steel fins for better conductivity and withstand temperatures up to 400°C.

  • Extruded finned tubes

An extruded finned tube is great for high temperature conditions and corrosive atmospheric conditions. Extruded tubes are often used in heat pipes, dry air coolers, air to air heat exchangers (HVAC), air dehumidification, energy recovery and offshore and remote applications.

HF welded fins

High frequency welded helical finned tubes are ideal for various industrial applications, including petrochemical and power generation. With this type of heat exchanger tube, the helical fin is attached to the base by electric resistance welding and provides a homogeneous, clean bond for efficient heat flow and corrosion resistance.

Common uses of HF welded fins include:

  • boilers
  • fired heaters
  • furnaces
  • heat exchangers
  • heat pipes

Integral fins

When it comes to improving the heat transfer between fluids, whilst keeping physical size and cost to a minimum, integrally finned tubes are an excellent choice. As their name suggests, the fin is integral with the tube and rolled out from the tube wall, reducing the thickness of the wall beneath the finned section.

Integrally finned tubes are available in:

  • carbon and low alloy steel
  • stainless steel
  • copper alloys
  • titanium
  • high nickel alloys

Longitudinal fins

The fins for longitudinal finned tubes are resistance-welded in diametrically opposed pairs – making them extremely efficient. Formed from a u-channel, the base is pressure rolled and spot welded to the tube and fins are always in multiples of 4.

A longitudinal finned tube is suitable for a wide range of applications, including heat exchangers, fire-rated heaters, gas coolers and tank heaters. It’s often constructed from weldable or brazable materials and supplied u-bent or in straight lengths.

Contact USEL Tubular Division

Need to know more about finned tube heat exchangers? USEL Tubular Division has the knowledge and expertise to guide and advise you.

They pride themselves on rapid turnaround times and can offer an emergency delivery service to suit urgent requirements. Find out more by calling 0191 587 1777 or email

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