Application range of carbon steel and stainless steel in sulfuric acid
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1. Carbon steels such as Q235B, 16MnR (old grade), and 20G (old grade): They can perform satisfactorily in SO2 and SO3 flue gases at temperatures below 450°C, as well as in concentrated acids at room temperature with a concentration of over 93%. For nicotinic acid with a content of over 20% at temperatures below 150°C, a flow rate of less than 0.5 m/s is preferable. 2. Common austenitic stainless steels such as 304, 316, 310: They are still suitable in H2SO4 with a concentration of less than 5% or greater than 93%, at temperatures below 50°C. The corrosion rate at 180±20°C in 99~100% H2SO4 is 0.04~0.1 mm/a. Its corrosion resistance, as well as its resistance to oxidation and sulfidation by high-temperature flue gases, are superior to those of carbon steel when the content of nicotinic acid is less than 20%.
In short: Carbon steel (such as Q235B, 16MnR, 20G, etc.) is suitable for use in: – Flue gas environments containing sulfur dioxide and sulfur trioxide at temperatures below 450°C; – Concentrated sulfuric acid at room temperature with a concentration of over 93%; – Fuming sulfuric acid at temperatures below 150°C and with a concentration of over 20%, provided that the flow rate is below 0.5 m/s. Stainless steel (304, 316, 310, etc.) is suitable for use in: – Sulfuric acid with a concentration of less than 5% or higher than 93%, at temperatures not exceeding 50°C; – Concentrated sulfuric acid at around 180°C with a concentration of 99–100%; – Fuming sulfuric acid with a concentration of less than 20%, where it offers better corrosion resistance compared to carbon steel, as well as greater resistance to oxidation and sulfidation caused by high-temperature flue gases. In general, carbon steel is suitable for environments with high-concentration sulfuric acid, low temperatures, and slow flow rates； Stainless steel has a wider range of applications; it can be used in both medium- and low-concentration as well as high-concentration sulfuric acids, but temperature control must be taken into account. .