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Table 1-1 Corrosion resistance properties of commonly used alloy pure metals Category name Corrosion resistance properties Notes Alloy 316SST 316LSST is a commonly used austenitic stainless steel. Compared with standard 302SST stainless steel, 316SST and 316LSST have better corrosion resistance to sulfuric acid, sulfide solutions, sodium and manganese salt solutions, hydrochloric acid solutions and phosphoric acid solutions than 302SST. They also have good corrosion resistance to acetic acid, formic acid, formic acid and hot alkali solutions. This type of steel has a low carbon content, so it does not require heat treatment after welding. Especially 316LSST, which is called ultra-low carbon stainless steel, has better intergranular corrosion resistance than 316SST, so it has better corrosion resistance. Not resistant to corrosion by hydrofluoric acid, wet chlorine gas, hydrochloric acid gas, iodine, bromine, etc. Monel alloy is one of the most resistant metals to hydrofluoric acid, besides platinum and silver. It can also be used as anti-corrosion material in chloride, sea water and alkali. It is not resistant to nitric acid, hydrochloric acid, high concentration or boiling sulfuric acid, and is not suitable for use in acidic iron salt, tin salt and other solutions. When a large amount of oxygen enters the measuring medium hydrofluoric acid, the corrosion resistance will decrease. In the case of high concentration of sodium hydroxide, the corrosion resistance is also poor. Hastelloy C Hastelloy C-276 has much higher corrosion resistance than ordinary austenitic stainless steel. Suitable for use in mixed liquids with a variety of corrosive media, such as wet chlorine, dry chlorine, nitric acid (<50°C), hydrochloric acid, sulfuric acid, phosphoric acid, acetic acid, hypochlorite, ferric chloride, copper chloride, caustic soda, seawater and various organic acids. Pure metal nickel is particularly resistant to alkali corrosion and is relatively stable at high temperatures or in molten alkali, so it is mainly used in the alkali production industry. At room temperature, nickel is extremely stable in seawater, salt solutions and organic media (such as fatty acids, phenols, alcohols, etc.). It is not resistant to inorganic acid corrosion and is unstable in acetic acid and formic acid. Titanium is a pure metal with very good corrosion resistance. In particular, it has strong corrosion resistance in various concentrations of nitric acid, organic acids, chlorides, wet chlorine and alkali. Not resistant to corrosion by relatively pure reducing acids and hydrochloric acid. Tantalum is a pure metal with high chemical stability. It has strong corrosion resistance in many corrosive media, such as inorganic acids, aqua regia, organic acids, chlorides, salts, corrosive gases, etc. Not resistant to hydrofluoric acid, fuming sulfuric acid, free sulfur trioxide, potassium iodide, fluoride ion solutions and strong alkali corrosion at high temperatures. Note: In order to improve the mechanical properties of pure metals, trace amounts of other metals are added as needed during the smelting process. Table 1-2. Reference table for corrosion resistance of materials in contact with media Classification Medium Name Concentration (%) Temperature Carbon Steel 316 Steel Hastelloy C Monel Tantalum Nickel Titanium Classification Medium Name Concentration (%) Temperature Carbon Steel 316 Steel Hastelloy C Monel Tantalum Nickel Titanium Inorganic Hydrochloric Acid 5RT BP ○ ○ ○○ ○● ● ○ ○Organic Salt Hydrofluoric Acid 5 48RT RT○ ○○ ○○ ○● ○ ○ 10RT BP ○ ○ ○○ ○● ● ○ ○ Acetic acid 100RT BP○ ○● ●● ●● ●● ● ● ● 20RT BP ○ ○ ○○ ○● ●○ ○ ○Formic acid 50RT BP○ ○○ ○● ● ● ● 35RT BP ○ ○ ○○ ○● ●○ ○○ ○Oxalic acid 10RT BP○ ○ ○● ● ○ ○○ ○ Sulfuric acid 5RT BP ● ○● ● ●●○ ○○ ○Citric acid 50RT BP○ ○● ●● ● ● ● 10RT BP ○ ○● ○● ● ●○ ○○ ○Alkaline caustic soda 20RT BP● ● ● ● ● ●● ●● 60RT BP○ ○ ● ○● ●●○ ○○ ○40RT BP● ● ● ● ○ ○● ● 80RT BP OO ○● ● ●● ●● ● 30RT BP○ ● ● ○○ ○● ●○ ○● ○Ammonium chloride 25RT BP○ ● ●● ● ● 68RT BP○ ● ● ○ ● ●○ ○● ●Calcium chloride 25RT BP ●● ●● ●● ● ● Fume RT ●○○Magnesium chloride 42RT BP ● ●● ● ● ● ● Phosphoric acid 30RT BP○ ○● ●●●● ○● ●○ ○ Sulfide sulfuric acid an20° saturated RT BP ● ● ● ● ●● ● 50RT BP○ ○● ● ●○ ○● ●○ ○ Sodium sulfide 10RT BP ● ●● ●● ● ● ● 70RT BP○ ○● ○● ○ ○● ●○ ○ Sodium sulfate 50RT BP ● ● ● 85RT BP○ ○● ○● ○○ ○● ●○ ○ Nitrate * ao acid an10RT BP● ● ●● ●○ ● ● 35%HCL+ 0.5%HNO3 RT ● Potassium phosphate all RT BP ● ● 90%HSO4+ 10%HNO3 RT ● Corrosive gas chlorine dry RT ●● ●●○ 70%HSO4+ 30%HNO3 RT ● Wet RT ○ ● ● 50%HSO4+ 50%HNO3 RT ● Chlorine water saturated RT ○ ● Chromium water 20RT BP ● ● ●○ ○ Sulfur dioxide wet RT BP ● ● Aqua regia HCL3 HNO31RT BP ○ ○● ○ ● ● Hydrogen sulfide wet RT ● ●○● Note: mark: ●Very good corrosion resistance. Average corrosion resistance. ○Poor corrosion resistance. Symbol: RT room temperature BP boiling point