The material of the main parts of the valve should first consider the physical properties (temperature, pressure) and chemical properties (corrosivity) of the working medium. At the same time, it is also necessary to know the cleanliness of the medium (whether there are solid particles). In addition, relevant regulations and requirements of the state and user departments shall also be referred to.
Many kinds of materials can meet the service requirements of valves under various working conditions. However, the most economical service life and the best performance of the valve can be obtained by correct and reasonable selection of valve materials.
Common material of valve body
1. Grey cast iron valves are widely used in various fields of industry because of their low price and wide scope of application. They are usually used in the case of water, steam, oil and gas as the medium, and are widely used in chemical industry, printing and dyeing, oiling, textile and many other industrial products that have little or no impact on iron pollution.
It is applicable to low pressure valves with a working temperature of – 15~200 ℃ and a nominal pressure of PN ≤ 1.6MPa.
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2. Black core malleable iron is applicable to medium and low pressure valves with working temperature between – 15~300 ℃ and nominal pressure PN ≤ 2.5MPa.
Applicable media are water, sea water, gas, ammonia, etc.
3. Nodular cast iron Nodular cast iron is a kind of cast iron, which is a kind of cast iron. The flake graphite in gray cast iron is replaced by the nodular graphite or globular graphite. The change of the internal structure of this metal makes its mechanical properties better than ordinary gray cast iron, and does not damage other properties. Therefore, valves made of ductile iron have higher service pressure than those made of gray iron. It is applicable to medium and low pressure valves with a working temperature of – 30~350 ℃ and a nominal pressure of PN ≤ 4.0MPa.
Applicable medium is water, sea water, steam, air, gas, oil, etc.
4. Carbon steel (WCA, WCB, WCC) initially developed cast steel to meet the production needs of those beyond the capacity of cast iron valves and bronze valves. However, due to the good service performance of carbon steel valves and their strong resistance to stresses caused by thermal expansion, impact load and pipeline deformation, their scope of use is expanded, usually including the working conditions of cast iron valves and bronze valves.
It is applicable to medium and high pressure valves with operating temperature of – 29~425 ℃. The temperature of 16Mn and 30Mn is between – 40~400 ℃, which is often used to replace ASTM A105. Applicable medium is saturated steam and superheated steam. High and low temperature oil products, liquefied gas, compressed air, water, natural gas, etc.
5. Low temperature carbon steel (LCB) Low temperature carbon steel and low nickel alloy steel can be used in the temperature range below zero, but can not be extended to the cryogenic area. Valves made of these materials are suitable for the following media, such as seawater, carbon dioxide, acetylene, propylene and ethylene.
It is applicable to low-temperature valves with operating temperature between – 46~345 ℃.
6. The valves made of low alloy steel (WC6, WC9) and low alloy steel (such as carbon molybdenum steel and chromium molybdenum steel) can be used for many working mediums, including saturated and superheated steam, cold and hot oil, natural gas and air. The working temperature of carbon steel valve can be 500 ℃, and that of low alloy steel valve can be above 600 ℃. At high temperature, the mechanical properties of low alloy steel are higher than that of carbon steel.
High temperature and high pressure valves applicable to non corrosive medium with operating temperature between – 29~595 ℃; C5 and C12 are applicable to high-temperature and high-pressure valves for corrosive media with operating temperature between – 29 and 650 ℃.
7. Austenitic stainless steels Austenitic stainless steels contain about 18% chromium and 8% nickel. 18-8 austenitic stainless steel is often used as valve body and bonnet material under high and low temperature and strong corrosion conditions. Adding molybdenum to 18-8 stainless steel matrix and slightly increasing nickel content will substantially increase its corrosion resistance. The valves made of this steel can be widely used in chemical industry, such as conveying acetic acid, nitric acid, alkali, bleach, food, fruit juice, carbonic acid, tanning liquid and many other chemical products.
In order to apply to the high temperature range and further change the material composition, niobium is added to the stainless steel, which is known as 18-10-Nb. The temperature can be 800 ℃.
Austenitic stainless steel is usually used at very low temperatures and will not become brittle, so valves made of this material (such as 18-8 and 18-10-3Mo) are very suitable for working at low temperatures. For example, it transports liquid gas, such as natural gas, biogas, oxygen and nitrogen.
It is applicable to valves with corrosive medium with operating temperature between – 196~600 ℃. Austenitic stainless steel is also an ideal low temperature valve material.
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8. Plastics and ceramics are both non-metallic materials. The biggest feature of non-metallic material valves is their strong corrosion resistance, and even have the advantages that metal material valves cannot have. It is generally applicable to corrosive media with nominal pressure PN ≤ 1.6MPa and working temperature not exceeding 60 ℃, and non-toxic SINGLE UNION BALL VALVE are also applicable to water supply industry. The material of the main parts of the valve should first consider the physical properties (temperature, pressure) and chemical properties (corrosivity) of the working medium. At the same time, it is also necessary to know the cleanliness of the medium (whether there are solid particles). In addition, relevant regulations and requirements of the state and user departments shall also be referred to.
Many kinds of materials can meet the service requirements of valves under various working conditions. However, the most economical service life and the best performance of the valve can be obtained by correct and reasonable selection of valve materials.
Post time: Feb-28-2023