Edited by CAI ZHONG CHAO
Stainless steel is resistant to most acids and bases, such as nitric acid and acetic acid, but sulfuric acid attacks stainless steel. Different concentrations of sulfuric acid have different corrosion effects on stainless steel, and stainless steels with different compositions are also different. This article mainly discusses the effects of different concentrations of sulfuric acid on stainless steel 304 and 316L, and how to prevent sulfuric acid from eroding stainless steel.
2. Stainless steel introduction:
304: Universal model, 18/8 stainless steel. China current national label is 06Cr19Ni10, replacing the previous 0Cr18Ni9. The standard composition is 18% chromium plus 8% nickel. It is stainless steel that is non-magnetic and cannot be changed by heat treatment.
316L: 316 is the second most widely used steel grade after 304, mainly used in the food industry and surgical equipment, adding molybdenum to obtain a special structure that is resistant to corrosion. Grade 18/10 stainless steels generally also meet this application level. Especially used in chemical, seaside, other corrosive environments, ship assembly, and building materials. 316L is a low carbon and more corrosion resistant. 316L stainless steel has good corrosion resistance at room temperature with a sulfuric acid concentration of less than 15% or greater than 85%. There is a certain temperature fluctuation above 80 degrees, and its corrosion resistance is greatly reduced. The corrosion resistance of 316L stainless steel itself is relatively poor in 45% dilute sulfuric acid medium, and its corrosion resistance is even worse if there is a certain temperature fluctuation.
3. Sulfuric acid is used in industry:
As one of the strong corrosive media, sulfuric acid is a very widely used industrial raw material. But different concentrations and temperatures of sulfuric acid, the corrosion of the material is quite different. For concentrated sulfuric acid with a concentration of more than 85% and a temperature of less than 80 °C, carbon steel and cast iron have better corrosion resistance, but it is not suitable for high-speed flowing sulfuric acid. Ordinary stainless steel such as 304, 316 sulfuric acid medium is also limited in use. Therefore, the delivery of sulfuric acid is usually made of high-silicon cast iron and high-alloy stainless steel. Fluoroplastics have better resistance to sulfuric acid, and fluorine-lined manufacturing is a more economical choice. We tested the ceramic coating, and the results showed that it has good resistance to diluting sulfuric acid, but the cost of ceramics is high, and there are cost considerations.
The sulfuric acid solution with a concentration of 15% to 85% has a high degree of corrosion on stainless steel. Although the resistance of 316L is stronger than that of 304, it will still be corroded. The temperature has a stronger effect on corrosion. At present, it is known that fluorine-lined manufacturing and ceramic cladding can be used, but through experience, fluorine will peel off and cause the inner stainless steel to be eroded. Although ceramics have good corrosion resistance, the cost will be one of the considerations.
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