1、 Determine the core material based on the corrosiveness of the material

1. Ordinary neutral/weakly corrosive materialsFor conventional organic solvents such as ethanol and acetone, 304 stainless steel is preferred. It has basic corrosion resistance and excellent cost-effectiveness, which can meet the requirements of conventional distillation conditions.

2. Chlorine containing, weakly acidic/weakly alkaline materials316/316L stainless steel is preferred for scenarios such as saltwater systems, dilute hydrochloric acid, and dilute alkali solutions. 316L has a higher molybdenum content and significantly better resistance to pitting and crevice corrosion than 304, making it particularly suitable for distillation systems containing chloride ions.

3. Highly corrosive materialsWhen dealing with concentrated acid, strong oxidizing agents and other media, ordinary stainless steel is not capable, and duplex stainless steel (such as 2205) or Hastelloy alloy can be used. Dual phase stainless steel combines austenitic and ferritic characteristics, with balanced corrosion resistance and mechanical properties; Hastelloy has stronger corrosion resistance but higher cost.

2、 Refine the brand by combining operating temperature and pressure

1. Low temperature distillation conditionsWhen the temperature is below -20 ℃, low-carbon stainless steel with excellent low-temperature toughness, such as 304L and 316L, should be selected to effectively avoid the risk of low-temperature brittle fracture of ordinary stainless steel.

2. High temperature and high pressure distillation conditionsWhen the temperature is above 400 ℃ and the pressure is greater than 1.6MPa, heat-resistant stainless steel (such as 310S) is preferred. Its high chromium nickel content gives it good high-temperature oxidation resistance and structural stability, preventing tower deformation or corrosion.

3、 Matching material cleanliness level requirements

1. Pharmaceutical and food grade distillation systemFor scenarios such as pharmaceutical solvent purification and food flavor separation, food grade 304/316L stainless steel should be selected. The surface of the material should be free of impurities, easy to polish, and comply with industry cleanliness standards such as GMP to avoid material contamination.

2. Electronic grade high-purity material distillationUltra high purity stainless steel should be selected to reduce the impact of impurity elements in the material on its purity.

4、 Differentiated selection of materials based on the functions of tower components

1. Tower shellTaking overall corrosion resistance and structural strength as the core, and referring to the principles of materials and working conditions mentioned above, materials such as 304, 316L, and duplex steel are selected.

2. Tower internalsWhen materials are prone to scaling or wear, 316L can be used for packing, tray, downcomer, etc. and surface hardening treatment can be carried out; When it is necessary to enhance separation efficiency, 316L precision machined parts with smooth surfaces and smooth flow channels should be preferred.

3. Takeover and flangeThe material should be compatible with the tower body to avoid electrochemical corrosion caused by welding of dissimilar steels, while also considering the sealing and temperature and pressure resistance of the connecting parts.

5、 Balancing cost and service life

1. When the working conditions are mild and the materials have no strong corrosion, 304 stainless steel is preferred to control the initial cost; When the corrosion risk is high, it is recommended to use 316L. Although the initial investment is high, it can reduce the comprehensive cost of later maintenance and replacement.

2. Large distillation towers can adopt the "composite plate" scheme: the base layer is made of carbon steel to ensure strength, and the cladding is made of stainless steel such as 316L to ensure corrosion resistance, achieving a balance between cost-effectiveness and anti-corrosion requirements.

6、 Meets industry standards and certification requirements

1. Corresponding industry standards must be met, such as GB/T 24511 stainless steel plate standard in the chemical industry and GB 4806 stainless steel standard for food contact in the pharmaceutical and food industries.

2. When it comes to exporting equipment, it is necessary to match international standards such as ASTM and EN to ensure that material certification is consistent with project acceptance requirements.