3. Non-corrosive conditions
When the valve working medium is water, steam, air, oil and other non-corrosive substances, carbon steel is generally used. Carbon steel for valves refers to WCB, WCC cast steel and ASTM A105 forged steel in the ASTM A216 standard. The suitable working temperature of carbon steel for valve is -29～425℃. However, for safety, considering that the working temperature of the medium may fluctuate, the operating temperature of carbon steel should not exceed 400°C in general.
4. Corrosion conditions
4.1 Chromium-molybdenum series high temperature steel
The Cr-Mo high temperature cast steel selected for the valve mainly uses WC6, WC9 and C5 (ZG1Cr5Mo) in the ASTM A217 standard, and the corresponding rolling materials are F11, F22 and F5 in the ASTM A182 respectively.
⑴Low chromium grade chromium-molybdenum steel
Low chromium grade chromium-molybdenum steels include WC6, WC9, F11 and F22, and their applicable working media are water, steam and hydrogen, and are not suitable for use in sulfur-containing oils. The suitable working temperature for WC6 and F11 is -29～540℃, and the suitable working temperature for WC9 and F22 is -29～570℃.
Chromium five molybdenum high temperature steel
There are C5 (ZG1Cr5Mo) and F5 chromium five molybdenum high temperature steels, and its applicable working media are water, steam, hydrogen, and sulfur-containing oils.
If C5 (ZG1Cr5Mo) is used in water vapor, its maximum working temperature is 600℃. When used in working media such as sulfur-containing oils, its maximum working temperature is 550°C. Therefore, it is stipulated that the working temperature of C5 (ZG1Cr5Mo) is≤550°C.
4.2 Stainless and acid-resistant steel
Stainless acid-resistant steel refers to chromium-nickel or chromium-nickel-molybdenum stainless, acid-resistant steel used in the petrochemical, chemical, and fertilizer industries for corrosion resistance such as nitric acid, sulfuric acid, acetic acid and organic acids. Stainless and acid-resistant steel cast steel mainly adopts CF8, CF8M, CF3, CF3M, CF8C, CD-4MCu and CN7M in the ASTM A743 or ASTM A744 standard, and the corresponding rolling materials are F304, F316, F304L in the ASTM A182 standard. , F316L, F347, F53 and United States UNS N08020.
⑴Cr-Ni stainless steel
Cr-Ni stainless acid-resistant steels include CF8, CF3, F304, F304L, CF8C and F347, which are suitable for oxidizing acids such as nitric acid as the working medium. Its maximum working temperature is≤200℃.
（2）Cr-Ni-Mo stainless steel
Cr-Ni-Mo stainless acid-resistant steels include CF8M, CF3M, F316 and F316L, which are suitable for reducing acids such as acetic acid as the working medium.
CF8M, CF3M, etc. can replace CF8 and CF3, but CF8 and CF3 cannot replace CF8M and CF3M. Therefore, the United States and other countries mainly use CF8M and CF3M for stainless and acid-resistant steel valves, and their maximum operating temperature is less than or equal to 200°C.
CN7M alloy has good overall corrosion resistance, it is widely used in harsh corrosive conditions, including sulfuric acid, nitric acid, hydrofluoric acid and dilute hydrochloric acid, caustic alkali, sea water and hot chloride salt solutions, etc., especially available It can be used in sulfuric acid with various concentration and temperature≤70℃. The service temperature of CN7M and UNS N08020 alloy is -29～450℃.
⑷Duplex stainless steel
Duplex stainless steels (Table 1) are precipitation hardening stainless steels. They contain 35% to 40% austenite in the ferrite matrix, and their yield strength is about 2 of that of 19Cr-9Ni austenitic stainless steel. Times, and has high hardness and good plasticity and impact toughness. It is especially suitable for use under both abrasion and erosion conditions. Therefore, it is widely used in strong acid conditions of oxidation and reduction, and has special resistance to stress corrosion cracking in a chlorine environment. The service temperature of CD-4MCu, CD3MN, CE3MN and F53 duplex stainless steel is -29～316℃.
4.3 Corrosion-resistant nickel-based alloys
Corrosion-resistant nickel-based alloy valves mainly use cast Monel (M35-1), cast nickel alloy (CZ-100), Inconel (CY-40), Hastelloy B (N-12MV) in the ASTM A494 standard. , N-7M) and Hastelloy C (CW-12MW, CW-7M, CW-6MC, CW-2M).
The Monel alloy rolled materials used for corrosion-resistant Monel alloy valves are mainly UNS N04400 (Monel 400) and UNS N05500 (Monel K500). There is no corresponding rolling material for cast nickel alloy, and the rolling material of Inconel alloy is Inconel 600 and Inconel 625.
Monel alloy (Monel) has high strength and toughness, especially has excellent resistance to reducing acid and strong alkali media and sea water and other corrosion properties. Therefore, it is usually used to manufacture equipment and valves for transporting hydrofluoric acid, salt water, neutral media, alkali salts and reducing acids. It is also suitable for dry chlorine, hydrogen chloride, high temperature chlorine at 425°C and high temperature hydrogen chloride at 450°C, etc. Medium, but not resistant to corrosion by sulfur-containing media and oxidizing media (such as nitric acid and media with high oxygen content). The valve material code is MM for the whole Monel alloy, and the internal parts are Monel alloy valves. When the shell is carbon steel, the valve material code is C/M, and when the shell is CF8, the valve material code is P/M, shell When the body is CF8M, the valve material code is R/M. The suitable working temperature of Monel alloy M35-1, Monel 400 and Monel K500 alloy is -29～480℃.
（2）Cast nickel alloy
The chemical composition of cast nickel alloy (CZ-100) is 95% Ni and 1.00% C, and there is no corresponding rolling material. When CZ-100 is used in high temperature, high concentration or anhydrous alkali solution, it has excellent corrosion resistance. CZ-100 is often used in the production of chlor-alkali with high corrosion concentration (including molten anhydrous caustic soda) and in the occasions where there is no metal pollution products such as copper and iron. The material code of the cast nickel alloy CZ-100 valve is Ni. The suitable working temperature of CZ-100 alloy is -29～316℃.
Inconel alloy (Inconel) CY-40 and Inconel 600 (ASTM B564 N06600) are mainly used for stress corrosion resistance, especially suitable for high concentration chloride media. When the Ni content is≥45%, the stress corrosion of chloride is "Immunity" effect. In addition, it is also resistant to corrosion by boiling concentrated nitric acid, fuming nitric acid, high-temperature gases containing sulfur and vanadium, and combustion products.
Inconel alloy has been widely used in the manufacture of boiler water supply system components in nuclear power plants because it is safer than stainless steel. At the same time, it is also suitable for industrial production that requires high-strength, high-pressure sealing and high corrosion resistance, as well as resistance to mechanical wear and oxidation at high temperatures. For example, large chemical fertilizer plants use Inconel 600 or Inconel 625 alloy (which is a rolled grade of Hastelloy CW-6MC) to manufacture high-pressure (600-1500LB) high-concentration oxygen valves, etc. The material code of CY-40 and Inconel 600 alloy valves is In. The suitable working temperature is -29~650℃.
Hastelloy (Hastelloy) is a commercial name, it includes a series of alloy grades, used in corrosion-resistant valves are mainly Hastelloy B (Hastelloy B) and Hastelloy C (Hastelloy C) two types.
Hastelloy B (Hastelloy B) casting alloy grades are N-12MV (N-12M-1) and N-7M in the ASTM A494 standard (some materials call it N-12M-2, also known as Chlorimet2 alloy) ), the grade of the rolled material is UNS N10665 in the ASTM B335 standard. Hastelloy B is resistant to various concentrations of hydrochloric acid, and is also resistant to non-oxidizing salts and acids. For corrosion-resistant valves of Hastelloy B, low-carbon Hastelloy B (N-7M) should be used in consideration of corrosion resistance and intergranular corrosion resistance. The material code of Hastelloy alloy has no regulations in the valve industry. The material code of Hastelloy B valve can be directly expressed by its cast alloy grade. The suitable working temperature of Hastelloy B is -29℃～425℃.
Hastelloy C (Hastelloy C) cast alloy grades are CW-12MW (some materials call it CW-12M-1) and CW-7M (CW-12M-2, also call it Chlorimet3 alloy) and Hastelloy C -276 alloy, its cast alloy grades are CW-6MC and Hastelloy C-4 alloy, and its cast alloy grade is CW-2M. Cast Hastelloy CW-7M, CW-12MW, CW-6MC and CW-2M have corresponding rolling material grades respectively UNS N10001, UNS N10003, UNS N10276 and UNS N06455. Hastelloy C is resistant to oxidizing solvents, low-concentration normal temperature hydrochloric acid and nitric acid.
The first generation of Hastelloy C (0Cr16Ni60Mo16W4) is characterized by excellent corrosion resistance in strong corrosive oxidizing and reducing acid media, but because the high nickel corrosion-resistant alloy is an austenitic structure, because Ni reduces C in The solid solubility in austenite and other reasons. Therefore, both the Ni-Mo series Hastelloy B and Ni-Mo-Cr series Hastelloy C alloys have a serious tendency or sensitivity to intergranular corrosion, which can also cause stress corrosion and crevice corrosion at high temperatures. In order to overcome the intergranular corrosion, the second generation Hastelloy alloy-Hastelloy C-276 (C is reduced from 0.03% to 0.02%) and the third generation Hastelloy C-Hastelloy C-4 are introduced, which are characterized by low Si (Si≤0.08%) and ultra-fine C (C≤0.015%), and reduce the content of Fe and W, and add stabilized alloying elements such as Ti.
For the corrosion-resistant valve of Hastelloy C, from the perspective of corrosion resistance and intergranular corrosion resistance, Hastelloy C-276 (CW-6MC) and Hastelloy C-4 (CW-2M) should be used. Hastelloy C valves have many material codes, and the performance and working temperature are very different, so CW-12MW, CW-7M, CW-6MC and CW-2M use HC-12, HC-7, HC-276 and HC- respectively. 4 means, or directly use its cast alloy grade to express.
The suitable working temperature of Hastelloy CW-7M and UNS N10001 alloy is -29～425℃, the suitable working temperature of Hastelloy CW-12MW and UNS N10003 alloy is -29～700℃, Hastelloy CW-6MC and UNS The suitable working temperature of N10276 alloy is -29～676℃, and the suitable working temperature of Hastelloy CW-2M and UNS N06455 alloy is -29～425℃.
4.4 Titanium alloy
Titanium (Ti) has high strength, light weight, sufficiently high heat resistance and low temperature toughness, and good processing and welding properties. Used in valve production mainly for casting pure titanium and forging pure titanium ZTA2.
Titanium exhibits corrosion resistance, intolerance to corrosive media due to different working conditions such as temperature, and even fires and explosions. Therefore, the nature (concentration, temperature, etc.) of the medium used should be clearly specified when ordering and designing.
The valve made of titanium has excellent corrosion resistance in a variety of oxidizing and corrosive media and neutral media.
Titanium has excellent corrosion resistance in nitric acid with a concentration below the boiling point and a concentration of≤80%. In fuming nitric acid, when the NO2 content exceeds 2% and the water content is insufficient, titanium reacts with fuming nitric acid and explodes. Therefore, titanium is generally not used for high-temperature nitric acid with a content of more than 80%.
Titanium is not resistant to corrosion in sulfuric acid, and titanium has moderate corrosion resistance in hydrochloric acid. It is generally believed that industrial pure titanium can be used in hydrochloric acid with a concentration of 7.5% at room temperature, 3% at 60°C, and 0.5% at 100°C. Titanium can also be used at a concentration of 30% at 35°C, 10% at 60°C, and 100°C. In phosphoric acid with a concentration of 3% at℃.
Titanium is not resistant to corrosion in HF (hydrofluoric acid), titanium is not resistant to corrosion in acidic fluoride solutions, titanium is resistant to corrosion in boric acid and chromic acid, and can be used in hydroiodic acid and hydrobromic acid.
Titanium can be used in the mixed acid of 10% sulfuric acid and 90% nitric acid at 60℃, the mixed acid of boiling 1% hydrochloric acid and 5% nitric acid, and room temperature aqua regia (Note: Aqua regia is a mixture of 3 volumes of concentrated hydrochloric acid and 1 volume of concentrated nitric acid) in.
Titanium is completely corrosion-resistant in various concentrations of barium hydroxide, calcium hydroxide, magnesium hydroxide, sodium hydroxide and potassium hydroxide solutions at room temperature, but it cannot be used in boiling sodium hydroxide and potassium hydroxide. Ammonia in the alkali will aggravate the corrosion of titanium.
The maximum working temperature of titanium in tap water, river water and air is 300℃. Titanium can be used in seawater with a maximum flow rate of 20m/s. Titanium has high corrosion resistance in seawater at a temperature of≤120℃. If the temperature is higher than 120℃, pitting corrosion and crevice corrosion may occur.
In addition to formic acid, oxalic acid and more concentrated citric acid (concentration≥50%), titanium has excellent corrosion resistance to all organic acids, but when the water content in the organic acid is too low (<0.1%), titanium is easy to Pitting corrosion occurs.
Titanium has excellent corrosion resistance in hydrocarbons and chlorinated hydrocarbons. Titanium can react violently in dry chlorine to produce TiCl4, and there is a danger of fire, but titanium has good corrosion resistance in wet chlorine (water content of 0.3 to 1.5%).
Titanium is stable in dry HCl at 20-160°C, but hydrochloric acid in wet hydrogen chloride will corrode titanium.
The pitting potential of titanium in chloride solution is higher than that of stainless steel, and the pitting corrosion resistance of titanium against chloride ions is better than that of stainless steel. Therefore, titanium has been widely used in chloride solution.
Titanium generally does not produce pitting corrosion when the temperature is less than or equal to 80℃, but in high temperature and moderate concentration chloride solution (such as 25% aluminum chloride solution at 100℃, 70% calcium chloride solution at 175℃, 25% at 200℃Pitting corrosion is more likely to occur in magnesium chloride solution and 75% zinc chloride solution at 200°C.