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This post was last edited by JS Chemical Instrumentation on 2017-3-20 at 14:18. The material chosen for the valve core must be determined based on the nature of the medium; several factors can be taken into consideration. If the medium is non-corrosive, such as water, 45# steel or other low-alloy structural steels can be used. If it is a corrosive medium, it is essential to know factors such as the nature of the corrosion, temperature, and concentration. Generally, corrosion in acidic environments is more severe than that in alkaline environments. There are also many types of acids, such as hydrochloric acid, sulfuric acid, nitric acid, organic acids, and so on. Alkaline corrosion such as sodium hydroxide, potassium hydroxide, etc. In an acidic environment, it is essential to be aware of the properties of the acid, temperature, concentration, pH value, etc.; otherwise, corrosion can occur even if stainless steel is used. Pure hydrochloric acid is generally handled using Hastelloy materials, while sulfuric acid typically requires materials such as 316, 904, 841, 20# alloy, and high-silicon cast iron. For nitric acid, materials such as 304 and 2Cr13 are generally used, while for organic acids, materials such as 304 and 316 are commonly selected. In an alkaline environment, carbon structural steel can be used at normal temperatures, while stainless steel and similar materials can be used at high temperatures and high concentrations. The first common material is 316 or 316L; A321 is also a type of stainless steel, with the difference lying in its carbon content and thus its hardness. The second common material is 416 SST: it offers good resistance to corrosion by water and steam, and is often used in the steam feed systems of power plants; it is also frequently utilized for manufacturing valve cores and seats. Due to the high stress, surfacing and surface hardening treatments are not possible, and the hardness decreases when the operating temperature exceeds 427°C. The third common material is 17-4 PH: it has good corrosion resistance and high strength. It is often subjected to three types of hardening treatments (H900, 1075, 1150) and is used to manufacture valve cages, valve seats, valve plugs, and valve shafts. It tends to become brittle at high temperatures, and its use is prohibited above 800 F (427 C). The fourth common material is 440 SST, the stainless steel material with the highest hardness for control valves (HRC 60); it has good corrosion resistance, and its operating temperature should not exceed 427°C, as in the case of feedwater valves in power plant boilers. The fifth common material is ALLOY 6, which retains its excellent corrosion and wear resistance even at high temperatures, maintaining good performance under steam conditions up to 566°C. It is mainly used for surfacing valve cores and seats. It has poor cutting and casting properties as well as high costs, so it is not used in the manufacture of valve cages. Sixth material type: Copper alloys: Suitable for media such as water, seawater, oxygen, air, and oils with a PN value of ≤2.5 MPa, as well as steam at temperatures ranging from –40 to 250°C. Common grades include ZGnSn10Zn2 (tin bronze), H62, Hpb59-1 (brass), QAZ19-2, and QA19-4 (aluminum bronze). Seventh material: Carbon steel: Suitable for media such as water, steam, air, hydrogen, ammonia, nitrogen, and petroleum products, with a nominal pressure of PN≤32.0 MPa and temperatures ranging from –30 to 425°C. Common grades include WC1, WCB, ZG25, as well as high-quality steels 20, 25, 30, and low-alloy structural steel 16Mn. Eighth material type: Stainless acid-resistant steel: Suitable for media such as nitric acid and acetic acid at a nominal pressure of PN≤6.4 Mpa and a temperature of ≤200°C. Common grades include ZG0Cr18Ni9Ti, ZG0Cr18Ni10, ZG0Cr18Ni12Mo2Ti, and ZG1Cr18Ni12Mo2Ti. Ninth material: alloy steel, used for medium and high pressure applications. When the medium is water, steam, oil, etc., with a temperature not exceeding 450°C, 40Cr (chromium steel) is generally chosen. For high-pressure applications with media such as water and steam whose temperature does not exceed 540°C, 38CrMoALA nitrided steel can be selected. For high-pressure applications with steam media whose temperature does not exceed 570°C, 25Cr2MoVA chromium-molybdenum-vanadium steel is generally selected. Tenth material type: Heat-resistant steel. For high-temperature valves where the medium temperature does not exceed 600°C, martensitic heat-resistant steel such as 4Cr10Si2Mo and austenitic heat-resistant steel such as 4Cr14Ni14W2Mo can be used.