Categories: Furnace tubes
Published 27 Jun 2019

A unique type of radiant furnace tube has entered the market. Kanthal® AF Tubes outperform common NiCr tubes, and they are economical as well.

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After more than two years of preparation and testing, Kanthal® AF Tubes are in production.

“I’m proud that we can now offer this product on the market,” says Krister Wickman, global product manager for high-temperature tubes at Kanthal. “The Kanthal® AF Tube is a unique product that has extremely good resistance to oxidation and corrosion at elevated temperatures. There is nothing like it on the market today.”

Kanthal® AF Tubes are made from the proven Kanthal® AF alloy, a ferritic iron-chromium-aluminum (FeCrAl) alloy. The tubes are spiral-welded, meaning they are symmetrical and have the same properties from every angle. They are made for vertical installation and are ideal for furnaces used for case hardening.

The tubes’ thin wall reduces heat loss from the furnace as well as furnace heat-up time. It also speeds the transfer of heat from the heating element to the goods in the furnace.

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“A typical application would be in furnaces for heat treatment of components for the auto industry, where you carburize the surface to withstand wear,” Wickman says.

A tale of two alloys

The most common choices for these types of applications today are FeNiCr and NiCr tubes. During testing, Kanthal compared the two types of alloys.

“The tubes were subject to cyclic tests up to 1,100 degrees Celsius in our lab, where both conditions and temperatures were considered very stressful for any oxidation properties,” says Susanne Selin, senior R&D professional at Kanthal (Susanne is pictured on top of the page). “When we compared them with common NiCr alloy 310 tubes, there was a striking difference in the spallation of oxide. After testing, the NiCr tubes showed black oxide (chromia) with high levels of spallation, while the Kanthal® AF Tubes only showed slow growing, gray oxide (alumina) with no spalling.”

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Björn Holmstedt, technical center manager at Kanthal, says the lack of spallation would be a big advantage for any customer switching from conventional NiCr tubes to Kanthal® AF Tubes. “Spallation from NiCr tubes will contaminate customer goods and the heating element mounted inside the radiant tube, which will eventually cause element failure,” he says. “The spallation will contribute to reduced tube wall thickness on NiCr tubes over time. “Another advantage is that Kanthal® AF Tubes are much lighter than NiCr tubes, which makes them easier to handle for maintenance or installation.”

During testing, Kanthal® AF Tubes also showed very good performance regarding oxidation and were highly responsive thanks to the reduced wall thickness. Moreover, temperature uniformity proved to be very good.

Success at customer sites

Besides lab testing, Kanthal® AF Tubes have been put to the test at customer sites, with amazing results.

“The test results are fantastic,” Selin says. “After two years of use, they still look like new – there is no sight of corrosion, oxidation or elongation of the tubes. We are very pleased with the results.”

Selin says she is excited to see how the tubes are received on the market, since there has been demand for radiant tubes with better properties.

“We wanted to come up with a product with very good oxidation and corrosion properties at an affordable price,” Krister Wickman concludes. “Kanthal® AF Tubes will help our customers increase their productivity and reduce their furnace running costs. In other words, they will save both time and money.”

Main advantages...

...of the Kanthal® AF Tubes

  • Made from the proven Kanthal® AF alloy, a ferritic iron-chromium-aluminum (FeCrAl) alloy
  • Minimum corrosion and oxidation
  • Almost non-existent spallation/contamination of the heating element
  • Reduced heat loss from the furnace and faster furnace heat-up time compared to NiCr tubes, thanks to thin walls
  • Much lighter than NiCr tubes, i.e. easier to handle for maintenance or installation
  • Less need for service or replacement of both tubes and elements.

Read more

Find more information about Kanthal® AF radiant tubes in our Products section.