What material should be used for gaskets between flanges in the mixed acid plant?

The following is a comparison between metal gaskets and non-metallic gaskets for selection. Metal gasket materials: 1. Carbon steel: The recommended maximum operating temperature is not more than 538°C, especially when the medium is oxidizing. High-quality low-carbon steel plates are not suitable for use in equipment designed to handle inorganic acids or neutral or acidic salt solutions; if such carbon steel is subjected to stress, the accident rate in equipment operating under hot water conditions is very high. Carbon steel gaskets are commonly used in high-concentration acids and many alkaline solutions. Brinell hardness is about 120. 　　2.304 Stainless Steel: 18-8 (18–20% chromium, 8–10% nickel); the recommended maximum operating temperature is 760°C. Stress corrosion and intergranular corrosion tend to occur in the temperature range of -196 to 538°C. Brinell hardness 160. 　　3.304L stainless steel 　　Carbon content not exceeding 0. 03%. It is recommended that the maximum operating temperature not exceed 760°C. Its corrosion resistance is similar to that of 304 stainless steel. The low carbon content reduces the precipitation of carbon from the lattice, resulting in better resistance to intergranular corrosion compared to 304 stainless steel. Brinell hardness is about 140. 　　4.316 Stainless Steel: 18-12 (18% chromium, 12% nickel); it contains about 2% more molybdenum than 304 stainless steel, and its strength and corrosion resistance increase as the temperature rises. It exhibits higher creep resistance than other ordinary stainless steels when the temperature rises. It is recommended that the maximum operating temperature not exceed 760°C. Brinell hardness is about 160. 　　5.316L stainless steel: The recommended maximum continuous operating temperature is not exceeding 760°C to 815°C. The carbon content is such that it provides better resistance to stress and intergranular corrosion compared to 316 stainless steel. Brinell hardness is about 140. 　　6.20 alloy: 45% iron, 24% nickel, 20% chromium, and small amounts of molybdenum and copper. It is recommended that the maximum operating temperature not exceed 760°C to 815°C. It is particularly suitable for manufacturing equipment resistant to sulfuric acid corrosion, with a Brinell hardness of about 160. 　　7. Aluminum Aluminum (with a content of not less than 99%). Aluminum has excellent corrosion resistance and machinability, making it suitable for manufacturing double gasket inserts. Brinell hardness is about 35. The recommended maximum continuous operating temperature is not exceeding 426°C. 　　8. Red copper: The composition of red copper is similar to that of pure copper; it contains trace amounts of silver to increase its operating temperature under continuous use. It is recommended that the maximum continuous operating temperature not exceed 260°C. Brinell hardness is about 80. 　　9. Brass (66% copper, 34% zinc): It exhibits good corrosion resistance under most operating conditions, but is not suitable for use with acetic acid, ammonia, salts, and acetylene. It is recommended that the maximum continuous operating temperature not exceed 260°C. Brinell hardness is about 58. 　　10. Hastelloy B-2 (26-30% molybdenum, 62% nickel, and 4-6% iron). It is recommended that the maximum operating temperature not exceed 1093°C. It exhibits excellent resistance to corrosion by concentrated hydrochloric acid. It also exhibits excellent resistance to corrosion by humid hydrogen chloride gas, as well as by sulfuric acid, phosphoric acid, and reducing salt solutions. It possesses high strength under high-temperature conditions. Brinell hardness is about 230. 　　11. Hastelloy C-276: 16–18% molybdenum, 13–17.5% chromium, 3.7–5.3% tungsten, 4.5–7% iron; the remainder is nickel. It is recommended that the maximum operating temperature not exceed 1093°C. It has excellent corrosion resistance. It exhibits excellent corrosion resistance to various attempts using cold nitric acid or boiling nitric acid at a concentration of 70%, as well as good resistance to hydrochloric and sulfuric acid corrosion, along with outstanding resistance to stress corrosion. Brinell hardness is about 210. 　　12. Inconel 600 Nickel-based alloy (77% nickel, 15% chromium, and 7% iron). It is recommended that the maximum operating temperature not exceed 1093°C. It possesses high strength at high temperatures and is typically used in equipment where stress corrosion issues need to be addressed. It exhibits excellent formability at low temperatures. Brinell hardness is about 150. 　　13. Monel 400 　　(Copper 30%, nickel; the recommended maximum continuous operating temperature is not exceeding 815°C.) It exhibits excellent corrosion resistance to most acids and bases, except for strongly oxidizing acids. Stress corrosion cracks tend to occur in hydrofluoric acid, mercuric chloride, and mercury-based media; therefore, it is not suitable for use in these media. Equipment widely used in the production of hydrofluoric acid. Brinell hardness is about 120. 　　14. Titanium: The recommended maximum operating temperature is no more than 1093°C. It exhibits excellent corrosion resistance under high-temperature conditions. As is well known, it resists chloride corrosion, and exhibits excellent resistance to nitric acid corrosion over a wide range of temperatures and concentrations. Titanium is rarely used in most alkaline solutions and is suitable for oxidation conditions. Brinell hardness is about 216. II. Non-metallic gasket materials 1. Natural rubber NR It exhibits good corrosion resistance to weak acids and bases, as well as to salt and chloride solutions; however, its resistance to oils and solvents is poor, and it is not recommended for use in ozone-containing environments. Recommended operating temperature: -57°C to 93°C. 　　2. Neoprene CR Neoprene is a synthetic rubber that is resistant to corrosion by acids, bases, and salt solutions with moderate corrosivity. It provides excellent corrosion resistance for commercial oils and fuels. However, its corrosion resistance is poor in strongly oxidizing acids, aromatic hydrocarbons, and chlorinated hydrocarbons. Recommended operating temperature: -51°C to 121°C. 　　3. Nitrile rubber NBR Nitrile rubber is a synthetic rubber that exhibits good resistance to corrosion by oils, solvents, aromatic hydrocarbons, basic hydrocarbons, as well as petroleum and natural gas, over a wide temperature range. It exhibits good corrosion resistance to hydroxides, salts, and nearly neutral acids. However, its corrosion resistance is poor in strongly oxidizing media, chlorinated hydrocarbons, alcohols, and lipids; the recommended operating temperature is 51°C to 121°C. 　　4. Fluororubber: It exhibits good corrosion resistance to oils, fuels, chloride solutions, aromatic hydrocarbons, aliphatic hydrocarbons, and strong acids; however, it is not suitable for use with amines, fats, oils, and steam. The recommended operating temperature range is -40°C to 232°C. 　　5. Chlorosulfonylated polyethylene synthetic rubber exhibits good corrosion resistance to acid, alkali, and salt solutions, and is unaffected by climate, light, ozone, or commercial fuels such as diesel and kerosene. But it is not suitable for aromatic hydrocarbons, chlorinated hydrocarbons, chromic acid, and nitric acid. Recommended operating temperature: -45°C to 135°C. 　　6. Silicone rubber 　　It exhibits good corrosion resistance to hot air. Silicone rubber is not affected by sunlight and ozone. But it is not suitable for steam, similar substances, aromatic hydrocarbons, and lipid hydrocarbons. 　　7. Ethylene-propylene rubber: It exhibits good corrosion resistance to strong acids, strong bases, salts, and chloride solutions. But it is not suitable for oils, solvents, aromatic hydrocarbons, and hydrocarbons. Recommended operating temperature: -57°C to 176°C. 　　8. Graphite This is a pure graphite material that contains no resins or inorganic substances; it can be divided into graphite materials with metal additives or those without such additives. This material can be bonded to manufacture pipe gaskets with a diameter exceeding 600 MM. It exhibits extremely excellent corrosion resistance against many acids, bases, salts, organic compounds, heat transfer fluids, and even high-temperature solutions. It cannot melt, but it will sublimate at temperatures above 3316°C. Use of this material in strongly oxidizing media at high temperatures should be done with caution. In addition to being used for gaskets, this material can also be used to make packing and the non-metallic winding strips in spiral wound gaskets. 　　9. Ceramic fibers, especially those molded into strips, are excellent gasket materials suitable for high-temperature and low-pressure conditions as well as light flange applications. The recommended operating temperature is 1093°C, and they can be used to manufacture the non-metallic winding strips in spiral-wound gaskets. 　　10. PTFE combines the advantages of most plastic gasket materials, including a temperature resistance range of -95°C to 232°C. It exhibits excellent corrosion resistance to chemicals, solvents, hydroxides, and acids, in addition to free fluoride and alkali metals. PTFE material can be filled into glass in order to reduce its cold flow and creep properties.

Considering the issue of corrosion, if the temperature is below 100 degrees, it is recommended that you use rigid PTFE gaskets; our equipment’s acid systems all use PTFE gaskets. Under no circumstances should metal shims be used.