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How to choose valve materials in a chloride ion environment?
Created on 03.15
1. Type 304 stainless steel This is the cheapest and most widely used austenitic stainless steel (such as food, chemical, atomic energy and other industrial equipment). Suitable for general organic and inorganic media. For example, nitric acid with a concentration < 30% and a temperature ≤ 100°C or a concentration ≥30% and a temperature < 50°C; Carbonic acid, ammonia and alcohols in various concentrations at temperatures ≤ 100°C. Poor corrosion resistance in sulfuric acid and hydrochloric acid; It is particularly sensitive to crevice corrosion caused by chlorine-containing media such as cooling water.
2. The corrosion resistance and use of type 304L stainless steel are basically the same as those of type 304. Due to the lower carbon content (≤0.03%), it has better corrosion resistance (especially resistance to intergranular corrosion, including the weld area) and weldability, and can be used in half-welded or full-welded PHE.
3. Type 316 stainless steel is suitable for general organic and inorganic media. For example, natural cooling water, cooling tower water, demineralized water; carbonic acid; Acetic acid and caustic lye < 50% concentration; solvents such as alcohols and acetone; Dilute nitric acid (concentration < 20%), dilute phosphoric acid (concentration < 30%), etc. with a temperature ≤ 100°C. However, it should not be used for sulfuric acid. Because it contains about 2% Mo, it has better corrosion resistance in seawater and other chlorine-containing media than type 304, and can completely replace type 304.
4. The corrosion resistance and use of type 316L stainless steel are basically the same as those of type 316. Due to the lower carbon content (≤0.03%), the weldability and post-weld corrosion resistance are also better, and it can be used for half-welded or full-weld PHE.
5. Type 317 stainless steel is suitable for working conditions that require a longer service life than Type 316. Because the content of Cr, Mo and Ni elements is slightly higher than that of type 316, it has better resistance to crevice corrosion, pitting corrosion and stress corrosion.
6. AISI 904L or SUS 890L type stainless steel. This is a cost-effective austenitic stainless steel that balances price and corrosion resistance. Its corrosion resistance is superior to the materials mentioned above, making it particularly suitable for general sulfuric acid, phosphoric acid, and other acids and halides (including Cl-, F-). Due to its high content of Cr, Ni, and Mo, it exhibits good resistance to stress corrosion, pitting corrosion, and crevice corrosion.
7. Avesta 254 SMO high-grade stainless steel. This is an ultra-low-carbon high-grade stainless steel that has been enhanced from type 316 by increasing the Mo content. It offers excellent resistance to chloride pitting and crevice corrosion and is suitable for applications involving saltwater, inorganic acids, and other media that are incompatible with type 316.
8. Avesta 654 SMO high-grade stainless steel. This is an ultra-low-carbon high-grade stainless steel with Cr, Ni, Mo, and N content higher than 254 SMO, which has better resistance to chloride corrosion than 254 SMO and can be used in cold seawater.
9. RS-2 (OCr20Ni26Mo3Cu3Si2Nb) stainless steel, which is a domestic Cr–Ni–Mo-Cu stainless steel. The pitting and crevice corrosion resistance is equivalent to that of Type 316, while the stress corrosion resistance is better. It can be used for concentrated sulfuric acid (concentration 90~98%) below 80 °C, with an annual corrosion rate ≤ 0.04mm/a.
10. Incoloy 825 (S) This is a Ni(40%)–Cr(22%)–Mo(3%) high-grade stainless steel. Incoloy is a registered trademark of the International Nickel Co. It is suitable for various concentrations of sulfuric acid at low temperatures; In caustic alkali (such as NaOH) solution with a concentration of 50%~70%, it has good corrosion resistance and does not produce stress corrosion cracking. However, it is sensitive to crevice corrosion caused by chloride. In addition, the stamping performance is not very good, so it is not a commonly used material for plates. 11. Alloy 31: improved from 904L (increased Mo and N content), standard 6%Mo high-grade stainless steel (31%Ni-27%Cr-6.5%Mo-32%Fe). Corrosion resistance is better than 904L in many media; In sulfuric acid with a concentration of 20%~80% and a temperature of 60°C~100°C, the corrosion resistance even exceeds that of C-276.
12. Alloy 33: A fully austenitized chromium-based high-grade stainless steel with corrosion resistance comparable to some Ni-Cr-Mo alloys such as Inconel 625. In acidic and alkaline media (including nitric acid, a mixture of nitric acid and hydrofluoric acid), it has good resistance to local corrosion and stress corrosion cracking. The corrosion resistance in concentrated nitric acid is much better than that of 304L. For example, it is suitable for sulfuric acid with a concentration greater than 96%~99%, a temperature ≤ 150°C, and a sulfur oxide content of less than 200 mg/L; hot seawater; ≤ 50% concentration, boiling highly corrosive solution; Phosphoric acid with a concentration ≤ 85% and a temperature ≤ 150°C. However, it is not suitable for reducing media (such as dilute sulfuric acid, etc.). The price is about the same as that of C-276.
13. C-2000 alloy: A nickel-based alloy developed in the 1990s, priced similarly to C-276, and offering superior corrosion resistance among the aforementioned materials. It exhibits better corrosion resistance than C-276 and C-22 in media such as sulfuric acid, dilute hydrochloric acid, phosphoric acid at concentrations ≤ 50% and boiling temperatures below moderate concentrations, and hot chlorides. It is showing a trend towards replacing C-22 alloys. However, its corrosion resistance is inferior to C-276 in sulfuric acid at concentrations ≥ 70%.
14. Alloy 59: Compared with C-2000, the chemical composition is basically the same except for a slightly higher Ni content (59%), low Fe, no Cu and W. This is currently the best material in corrosion resistance, thermal stability, stampability and weldability among nickel-based alloys, and has been widely used in sulfuric acid, hydrochloric acid, hydrofluoric acid and many media containing chlorine, oxygen, and low pH since its commercialization in 1990.
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