Discuss the corrosion resistance of ordinary carbon steel and cast iron in sulfuric acid
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1) Ordinary carbon steel cannot withstand dilute sulfuric acid at concentrations below 80%, but it can tolerate concentrated sulfuric acid at concentrations of 80%–100% at around 65°C. Since carbon steel can form a passivation film within this concentration range, it can be used directly as a material for manufacturing equipment used for storing and transporting 80%–100% concentrated sulfuric acid under conditions of normal temperature, no flow, no erosion, no aeration, and in a sealed environment. No additional anti-corrosion treatment is required for the inner wall, while the outer wall only needs to be coated with a standard paint that provides resistance to mild corrosion and weathering. 2) Neither ordinary carbon steel nor cast iron can withstand sulfuric acid with a concentration of over 102%, so they cannot be used as materials for manufacturing storage tanks for such acid
Plain carbon steel is not suitable for use in dilute sulfuric acid with a concentration of 80% or less, as it cannot form an effective protective passivation film. However, in an environment with 80%-100% concentrated sulfuric acid, a passivation film can be formed, which allows such equipment to be used for storing and transporting sulfuric acid at this concentration. Moreover, these devices are subject to many usage constraints, such as requiring normal temperature, no flow of air, and a sealed condition. As for cast iron, similar to ordinary carbon steel, it cannot be used in storage equipment for fuming sulfuric acid (sulfuric acid with a concentration of over 102%). This is because under the attack of high-concentration sulfuric acid, neither can form a protective film, making them highly susceptible to corrosion and damage. .