When a fan handles wet, acidic or chloride-bearing gas, the material of the impeller and casing determines how long the fan lasts. DCS Cleantech builds centrifugal fans whose gas-wetted parts – impeller, casing and inlet cone – are made of duplex stainless steel EN 1.4462. Duplex has proven a good choice especially in biomass-fired heating plants, where the flue-gas fan runs after a scrubber or flue-gas condenser.
What is duplex steel?
Duplex stainless steel has a two-phase microstructure of roughly equal parts austenite and ferrite. The most widely used grade, EN 1.4462 (2205), contains about 22 % chromium, 5–6 % nickel, 3 % molybdenum and nitrogen. This combination gives properties that neither structural steel nor austenitic acid-proof steel (EN 1.4404 / 316L) offers on its own.
Five advantages in fan duty
- Twice the strength. The yield strength of duplex is about twice that of austenitic stainless steels. The impeller can be built lighter or run at a higher tip speed, which means lower rotor mass, lower bearing loads and more pressure from a given impeller size.
- Better resistance to pitting and crevice corrosion. The pitting resistance equivalent (PREN) of EN 1.4462 is at least 34, compared with about 24–26 for 316L. This matters in saturated flue gas, where condensate concentrates chlorides and acids on the impeller and casing walls.
- Resistance to stress corrosion cracking. The duplex microstructure resists chloride stress corrosion cracking far better than austenitic stainless steels. A rotating impeller is under constant stress, so this is often the deciding property.
- Corrosion fatigue and erosion. High strength combined with corrosion resistance gives duplex good corrosion-fatigue and erosion-corrosion properties – useful when the gas carries droplets, fly ash or fine sand.
- Lower life-cycle cost. A duplex impeller costs more to buy than a structural-steel one, but it needs no protective coating and stays in balance longer in corrosive duty. The payback comes from fewer impeller replacements and unplanned shutdowns.
Typical applications
- Flue-gas fans after scrubbers and flue-gas condensers in biomass and district-heating plants
- Sulphur scrubbers and other wet gas cleaning
- Flue-gas recirculation fans
- Wastewater treatment and odour control
- Process gases in the pulp and paper and chemical industries
When duplex is not the right choice
Duplex is not a material for hot gas: continuous service is limited to about +250 °C. For hotter gases we use heat-resistant steels, and for dry, highly abrasive dust wear-resistant steels such as Hardox. Where wear and corrosion occur together, the materials can be combined – for example a duplex outer shell with a replaceable Hardox wear liner, as in our Finn-Cleaner cyclones.
Made in Voikkaa
DCS designs and manufactures duplex fans and spare parts at its own workshop in Voikkaa. Welding duplex requires the right filler metals and controlled heat input to keep the austenite–ferrite balance; our workshop is certified to ISO 3834-2 for welding and operates an ISO 9001 quality system. We also make duplex impellers, casings and inlet cones for existing fans – including fans from other manufacturers – to the dimensions of the original part.
Request a quotation
Send us the gas data – flow, pressure rise, temperature, moisture content and composition – and we will propose the right fan and material. More about our fans: Premium fans.
DCS Cleantech Oy
sales@dcs.fi · +358 44 730 8110