One of the key issues that must be considered in valve design and material selection is the operating temperature of the valve. In order to standardize the suitable working temperature of the main material of the valve, the suitable working temperature of the main material of the valve used in my country's petrochemical, chemical, fertilizer, electric power and metallurgical industries from the aspects of the material properties of various types of valve steel and alloy grades and related The requirements have made clear regulations for the design, manufacture and inspection of valve products. In addition, from the aspects of technical management, production management and material procurement, each type of steel should be selected with good comprehensive performance, and it is not appropriate to use too many steel grades and alloy grades to prevent confusion.
1 Overview
One of the key issues that must be considered in valve design and material selection is the operating temperature of the valve. In order to standardize the suitable working temperature of the main material of the valve, the suitable working temperature of the main material of the valve used in my country's petrochemical, chemical, fertilizer, electric power and metallurgical industries from the aspects of the material properties of various types of valve steel and alloy grades and related The requirements have made clear regulations for the design, manufacture and inspection of valve products. In addition, from the aspects of technical management, production management and material procurement, each type of steel should be selected with good comprehensive performance, and it is not appropriate to use too many steel grades and alloy grades to prevent confusion.
Low temperature conditions
2.1 Cryogenic valve material
Ultra-low temperature valves [-254 (liquid hydrogen) ~ -101 ° C (ethylene)] The main material must be austenitic stainless steel, copper alloy or aluminum alloy with a face-centered cubic lattice. The low-temperature mechanical properties after heat treatment, especially low-temperature impact Toughness must meet the requirements of the standard.
The following austenitic stainless steels can be used to manufacture cryogenic valves. ASTM A351 CF8M, CF3M, CF8 and CF3, ASTM A182 F316, F316L, F304 and F304L, ASTM A433 316, 316L, 304, 304L and CF8D (designed by Lanzhou High Pressure Valve Factory, factory standard code GFQ81-93). The valve body, bonnet, gate or disc of the ultra-low temperature valve must be cryogenically treated in liquid nitrogen (-196°C) before finishing.
2.2 Cryogenic valve material
The main materials suitable for low-temperature valves (-100～-30℃) include low-temperature austenitic stainless steel and ferritic and martensitic steel for low-temperature pressure-bearing parts.
Austenitic stainless steels for low temperature include ASTM A351 CF8M, CF3M, CF8 and CF3, ASTM A182 F316, F316L, F304 and F304L, ASTM A433 316, 316L, 304, 304L and CF8D.
Ferritic and martensitic steels for low temperature pressure parts include ASTM A352 LCA (-32°C), LCB, LCC (-46°C), LC1 (-59°C), LC2, LC211 (-73°C) and LC3 ( -100°C).
The primary price of materials in the ASTM A352 standard is low, but the chemical composition must have reliable and very strict factory internal control standards during smelting. Its heat treatment process is complicated, and it needs multiple quenching and tempering treatments to meet the requirements of low-temperature impact toughness required by the standard, and the production cycle is long. When the low-temperature impact toughness does not meet the standard requirements, it is not allowed to be used as low-temperature steel. Therefore, it is only used when the production batch is large and can be smelted into a furnace, and austenitic stainless steel is generally used.
3. Non-corrosive working conditions
When the working medium of the valve is non-corrosive substances such as water, steam, air and oil, 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 valves is -29～425℃. However, for the sake of safety, considering that the working temperature of the medium may fluctuate, the service temperature of general carbon steel should not exceed 400°C.
4. Corrosion conditions
4.1 Chromium-molybdenum high temperature steel
The Cr-Mo high-temperature cast steel used for the valve mainly adopts 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.
⑴ Low chromium grade chromium-molybdenum steel
Low chromium grade chromium-molybdenum steels include WC6, WC9, F11 and F22. The applicable working medium is water, steam and hydrogen, and it is not suitable for sulfur-containing oil products. The suitable working temperature of WC6 and F11 is -29～540℃, and the suitable working temperature of WC9 and F22 is -29～570℃.
⑵ Chromium five molybdenum high temperature steel
Chromium five-molybdenum high-temperature steel has C5 (ZG1Cr5Mo) and F5, and its applicable working medium is water, steam, hydrogen and sulfur-containing oil, etc.
If C5 (ZG1Cr5Mo) is used for water vapor, its maximum working temperature is 600°C. When used in working media such as sulfur-containing oils, the maximum working temperature is 550°C. Therefore, it is stipulated that the operating temperature of C5 (ZG1Cr5Mo) is ≤550°C.
4.2 Stainless acid-resistant steel
Stainless acid-resistant steel refers to chromium-nickel or chromium-nickel-molybdenum stainless acid-resistant steel used in petrochemical, chemical, and fertilizer industries for corrosion resistance such as nitric acid, sulfuric acid, acetic acid and organic acids. The stainless and acid-resistant 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 US UNS N08020.
⑴Cr-Ni stainless steel
Cr-Ni stainless and 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℃.
⑵Cr-Ni-Mo stainless steel
Cr-Ni-Mo stainless and 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 stainless and acid-resistant steel valves in the United States and other countries mainly use CF8M and CF3M, and their maximum working temperature is ≤200°C.
⑶ CN7M alloy
CN7M alloy has good overall corrosion resistance, it is widely used in harsh corrosion conditions, including sulfuric acid, nitric acid, hydrofluoric acid and dilute hydrochloric acid, caustic alkali, seawater and hot chloride salt solution, etc., especially available In sulfuric acid with various concentrations and temperatures in the range of ≤70°C. The service temperature of CN7M and UNS N08020 alloy is -29～450℃.
⑷ Duplex stainless steel
Duplex stainless steel (Table 1) is precipitation hardening stainless steel, which contains 35% to 40% austenite in the ferrite matrix, and its yield strength is about 2 times 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 the corrosive working conditions of both abrasion and erosion, so it is widely used in strong acid working conditions of oxidation and reduction, and has special resistance to stress corrosion cracking in environments with chlorine. The service temperature of CD-4MCu, CD3MN, CE3MN and F53 duplex stainless steel is -29～316℃.
4.3 Corrosion-resistant nickel-based alloy
Corrosion-resistant nickel-based alloy valves are mainly cast Monel alloy (M35-1), cast nickel alloy (CZ-100), Inconel alloy (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 rolling materials used for corrosion-resistant Monel alloy valves are mainly UNS N04400 (Monel 400) and UNS N05500 (Monel K500). There is no corresponding rolled material for cast nickel alloy, and the rolled material of Inconel alloy is Inconel 600 and Inconel 625, etc.
⑴ Monel
Monel alloy (Monel) has high strength and toughness, especially has excellent corrosion resistance to reducing acid and strong alkali medium and seawater. Therefore, it is usually used to manufacture equipment and valves for conveying hydrofluoric acid, brine, neutral medium, alkali salt and reducing acid, and is also suitable for dry chlorine gas, hydrogen chloride gas, 425°C high temperature chlorine gas and 450°C high temperature hydrogen chloride gas, etc. Medium, but not resistant to corrosion of sulfur-containing media and oxidizing media (such as nitric acid and media with high oxygen content). The material code of the valve is Monel alloy as a whole, the code name of the valve material is Monel alloy, the code name of the valve material is C/M when the shell is carbon steel, and the code name of the valve material is P/M when the shell is CF8. 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℃.
⑵ Cast Nickel Alloy
The chemical composition of cast nickel alloy (CZ-100) is 95%Ni and 1.00%C, and there is no corresponding rolled 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 corrosive concentration (including molten anhydrous caustic soda) and in occasions where metals such as copper and iron cannot contaminate products. The material code of the cast nickel alloy CZ-100 valve is Ni. The suitable working temperature of CZ-100 alloy is -29～316℃.
⑶ Inconel alloy
Inconel alloy (Inconel) CY-40 and Inconel 600 (ASTM B564 N06600) are mainly used for stress corrosion resistance, especially for high-concentration chloride medium. When the Ni content is ≥ 45%, it has a strong effect on chloride stress corrosion "Immunity" effect. In addition, it can also resist the corrosion of boiling concentrated nitric acid, fuming nitric acid, high-temperature gas containing sulfur and vanadium, and combustion products.
Inconel alloy has been widely used in the manufacture of components for boiler feed water systems 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, high corrosion resistance, and resistance to mechanical wear and oxidation at high temperatures. For example, the large chemical fertilizer factory uses Inconel 600 or Inconel 625 alloy (the rolled product grade of Hastelloy CW-6MC) to manufacture high-pressure (600-1500 LB) 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℃.
⑷ Hastelloy
Hastelloy (Hastelloy) is a commercial name, which includes a series of alloy grades, mainly used for corrosion-resistant valves are Hastelloy B (Hastelloy B) and Hastelloy C (Hastelloy C).
The cast alloy grades of Hastelloy B (Hastelloy B) are N-12MV (N-12M-1) and N-7M in the ASTMA494 standard (some materials are called N-12M-2, also known as Chlorimet2 alloy ), and its rolling grade 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 selected 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℃.
The cast alloy grades of Hastelloy C (Hastelloy C) are CW-12MW (some materials are called CW-12M-1) and CW-7M (CW-12M-2, also known as Chlorimet3 alloy) and Hastelloy C -276 alloy, its casting alloy grade is CW-6MC and Hastelloy C-4 alloy, its casting alloy grade is CW-2M. Cast Hastelloy CW-7M, CW-12MW, CW-6MC and CW-2M correspond to rolling grades UNS N10001, UNS N10003, UNS N10276 and UNS N06455 respectively. Hastelloy C is corrosion-resistant to oxidizing solvents, low concentration hydrochloric acid and nitric acid at room temperature.
4.4 titanium alloy
Titanium (Ti) has high strength, light weight, sufficiently high heat resistance and low temperature toughness, and good processing performance and welding performance. It is mainly used for casting pure titanium and forging pure titanium ZTA2 in the production of valves.
Titanium exhibits corrosion resistance, non-corrosion resistance or even fire and explosion to corrosive media due to different working conditions such as temperature. Therefore, the nature (concentration, temperature, etc.) of the medium used should be clearly specified when ordering and designing.
Titanium valves have excellent corrosion resistance in a variety of oxidizing, highly corrosive and neutral media.
Titanium has excellent corrosion resistance in nitric acid below the boiling point and concentration ≤ 80%. In fuming nitric acid, when the NO2 content exceeds 2% and the water content is insufficient, the reaction between titanium and fuming nitric acid will explode. Therefore, titanium is generally not used in high-temperature nitric acid with a content of more than 80%.
Titanium is not corrosion resistant 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 30% at 35°C, 10% at 60°C and 100% at 60°C. In 3% phosphoric acid at ℃.