Author: YUHONG HOLDING GROUP CO., LTD (浙江宇鸿伟业特钢有限公司) — steelfintube.com, a manufacturer of finned tubes, boiler tubes and heat-exchanger tubes since 1990, exporting over 80% of its output.

As biomass boilers become increasingly common in the clean-energy sector, flue-gas waste-heat recovery has become a key route to higher boiler efficiency. The finned tube is the core heat-exchange component, and its material selection directly determines the service life and heat-transfer efficiency of the equipment. Biomass boiler flue gas has distinctive working conditions: combustion generates corrosive components such as sulfur compounds and chlorides; the flue-gas temperature is usually 120–140°C; in a low-temperature environment acidic condensate easily forms and triggers corrosion; and dust particles carried in the gas erode the tube wall. Finned-tube selection must therefore balance corrosion resistance, wear resistance and heat-transfer performance.

FAQ: Finned Tube Selection for Biomass Boiler Flue Gas

Q1: Why is material selection so critical in biomass boiler flue gas?

Because the working conditions are aggressive. Flue gas at 120–140°C combined with sulfur and chloride compounds falls below the acid dew point, forming a sulfuric acid condensate that corrodes the tube wall, while entrained ash erodes the surface. A material that ignores these conditions will fail prematurely.

Q2: Can carbon steel finned tubes (ASTM A106 / A179 / ASME SA-210) be used?

Carbon steel is a natural first consideration thanks to its good thermal conductivity, high mechanical strength, mature processing and a cost of only one-third to one-half of stainless steel — it performs well in ordinary low-temperature, non-corrosive duty. In ASME/ASTM terms, the base tube is typically ASTM A106 Gr.B, ASTM A179 or ASME SA-210 Gr.A1. However, biomass corrosion strikes exactly at carbon steel's weakness: ordinary carbon steel lacks corrosion-resistant alloying elements, and in sulfur-bearing low-temperature flue gas its corrosion rate can reach 0.35–1 mm per year. Within one to two years, wall perforation and fin corrosion or fracture appear, cutting waste-heat recovery efficiency and raising maintenance costs — so it is not suitable for long-term use.

Q3: Why is ASTM A588 low-alloy steel the ideal choice?

Cu-Cr low-alloy weathering steel conforming to ASTM A588 (Corten A) / ASTM A242 (Corten B) is purpose-designed for low-temperature acid dew-point corrosion resistance. By adding chromium and copper alloying elements, it forms a stable, dense, self-repairing passive layer in an acidic condensate environment, sharply reducing the sulfuric-acid corrosion rate — it is specifically suited to the low-temperature acid corrosion zone at the boiler tail. Its thermal conductivity is close to that of carbon steel, it has enough mechanical strength to withstand ash erosion, and its pressure-bearing performance matches the boiler system. This is why ASTM A588 / A242 low-alloy finned tubes are highly regarded in biomass boiler waste-heat recovery and are effective against the short-term corrosion and leakage seen with ordinary carbon steel.

Q4: When should stainless steel (ASTM A213 TP304 / TP316L) be used instead?

If the biomass fuel contains very high sulfur and chlorine and the working conditions are more severe, stainless steel finned tubes can be considered. The common grades — ASTM A213 TP304 (UNS S30400) and ASTM A213 TP316L (UNS S31603) — offer stronger corrosion resistance and tolerate extreme corrosive environments, but their cost is higher, so the choice should be weighed against both project budget and actual conditions.

Q5: Does the fin structure matter, or only the material?

Both matter. Biomass boiler flue gas carries a high dust load, and closely spaced fins clog and accumulate ash easily, reducing heat-exchange efficiency. The fin pitch should be chosen to keep the flue gas flowing smoothly and to minimise ash buildup.

Q6: What is the recommended selection strategy?

Selection must follow the actual working conditions. Prioritise ASTM A588 Cu-Cr low-alloy finned tubes to address low-temperature corrosion; choose stainless steel (ASTM A213 TP316L) for severe conditions; carbon steel (ASTM A106 / A179) can serve as a transitional option only for short-term, budget-limited use. Over the long term, the ASTM A588 low-alloy finned tube delivers the best balance of cost-effectiveness and reliability.