Stainless steel plates are widely used in various acid environments. In actual use, different types of stainless steel plates will be used according to the corrosive characteristics of different acids to maximize the service life of the material. Let’s talk about the application of stainless steel plates in various acid environments in detail.

Sulfuric acid environment

Chemical industries such as sulfuric acid, ammonium sulfate and synthetic fibers all use sulfuric acid as the basic raw material. Therefore, the corresponding devices use a large number of stainless steel plates. Low and medium concentrations of sulfuric acid are reducing acids, while hot concentrated sulfuric acid is a strong oxidizing acid. Therefore, different sulfuric acid concentrations and temperatures require different stainless steel plate specifications.

Generally, stainless steel plates containing 2-3% molybdenum are the lowest grade used in sulfuric acid. Type 18-8 stainless steel plates that do not contain molybdenum can only be used under certain conditions at room temperature. Stainless steel plates containing 2-3% molybdenum are used in In 5% sulfuric acid, it can be used up to 50℃; stainless steel plates containing 3-4% molybdenum can be used in 5% sulfuric acid at around 60℃; stainless steel containing molybdenum and copper has a wider range of use than stainless steel containing only molybdenum. Much wider. When sulfuric acid contains high-valent metal ions, it can form a great corrosion inhibition effect and expand the use range of some steels; when sulfuric acid contains activated ions such as F-, C1-, etc., it will significantly accelerate the corrosion of stainless steel plates, thereby causing the corrosion of some stainless steels. The range of use of the model is narrowed.

Nitric acid environment

The stainless steel plate is in this oxidizing acid because the oxide film formed on the surface of the stainless steel plate has excellent corrosion resistance. Therefore, stainless steel plates are widely used in nitric acid manufacturing equipment and various synthetic chemical industry equipment using nitric acid as raw material. Nitric acid corrosion is mainly uniform corrosion or intergranular corrosion, which basically does not lead to pitting corrosion and stress corrosion reactions. Therefore, all types of 18-8 stainless steel can be applied. For example, it can withstand nitric acid corrosion at any temperature with a concentration of ≤65% and normal pressure. When the concentration is ≤85%, 00Cr25Ni20Nb alloy should be used. When the concentration is ≥85% and fuming nitric acid, Generally, only high-silicon stainless steel plates can be used.

Phosphate environment

There are two main types of phosphoric acid production: wet method and thermal method. The phosphoric acid produced by the thermal method has better purity, while the phosphoric acid produced by the wet method will contain a certain amount of iron ions, chloride ions, etc. depending on the source of phosphate rock, industrial water, sulfuric acid and other raw materials. Stainless steel plates commonly used in pure phosphoric acid have good corrosion resistance. For example, 18-8 stainless steel can be used to store cold phosphoric acid with a concentration of up to 85%, while stainless steel plates containing 2-3% molybdenum have higher corrosion resistance. The equipment used to produce phosphoric acid by thermal method can use 18-8 or 18-12Mo2. For equipment that produces phosphoric acid by wet method, the chromium and molybdenum content of the selected material should be determined based on the chloride ions, iron ions, etc. in the phosphoric acid solution. It is usually a stainless steel plate with high chromium and molybdenum.

Hydrochloric acid environment

In hydrochloric acid aqueous solution, the combined action of chloride ions and hydrogen ions will destroy the passivation film on the surface of the stainless steel plate and prevent the formation of the passivation film, which can easily lead to uniform corrosion, pitting corrosion and stress corrosion cracking of the stainless steel plate. Special stainless steels such as Carpenter20 and Werthite cannot be used in hydrochloric acid and can only be used in very dilute hydrochloric acid.

sodium hydroxide environment

Although chromium-nickel austenitic stainless steels such as 18-8 and 18-12-Mo have good alkali corrosion resistance, they are prone to stress corrosion cracking, especially in moderate concentrations of NaOH. Therefore, nickel and manganese are the main alloying elements in the NaOH industry, and models such as 304, 304L, 316, and 316L can only be used in low-concentration solutions or low-temperature and high-concentration solutions.