1. Applications of Stainless Steel**Stainless steel (such as 304, 316, 321, 347, duplex steel, etc.) is commonly used in the petrochemical industry in the following scenarios:- **Atmospheric and vacuum device**: pipes, heat exchangers (316L chloride corrosion resistant).- Catalytic Cracking (FCC): Reactor internals (304/321 resistant to high temperature sulfur corrosion).- **Hydrotreating unit**: Reactor shell (347 stainless steel resistant to high temperature hydrogen corrosion).- **Acidic environment (including H₂S, CO₂)**: Duplex stainless steel (such as 2205) is used in oil and gas pipelines, separators.- Storage Tanks & Pipelines: 304/316 is used to store light oil, liquefied gas, etc.**Advantages**: low cost, good weldability, easy processing, suitable for medium corrosive environments.

2. Applications of nickel-based alloys** Nickel-based alloys (e.g. Inconel, Hastelloy, Monel, etc.) are used in more demanding conditions: - High Temperature and High Pressure Reactors: Inconel 600/625 is used for hydrogenation reactor internals. - **Sour Oil & Gas Extraction**: Hastelloy C-276 Resistant to Wet H₂S, Chloride Stress Corrosion. - Ethylene cracking furnace: Incoloy 800H/802 is resistant to high temperature oxidation and carburising. - **Offshore Platform**: Monel 400 is resistant to seawater corrosion and is used in pump valves, heat exchangers. - Sulfur Recovery Unit (Claus Process): Hastelloy B-2 is resistant to sulfuric acid dew point corrosion. **Advantages**: Excellent performance in extreme temperatures (up to 1200°C), high stress, strong acids (e.g. sulfuric acid, hydrochloric acid) or alkaline environments.

3. Basis of Selection**- Corrosion Type:- Chloride stress corrosion: Choose duplex steels or nickel-based alloys (e.g., C-276).- High-temperature vulcanization: select alloys containing chromium-nickel (e.g., 625).- **Temperature and pressure**: Nickel-based alloys are preferred for high temperature and high pressure (such as hydrocracking).- Economy: Stainless steel is suitable for mild corrosion, and nickel-based alloys are used in critical equipment.