Selection of valve material
Published：2020-03-13 16:23 Author：admin
When selecting the material of the main parts of the valve, the physical properties (temperature, pressure) and chemical properties (corrosiveness) of the working medium should be considered first. You should also know how clean the media is (with or without solid particles). In addition, it is also necessary to refer to the relevant regulations and requirements of the country and the user department.
Many kinds of materials can meet the requirements of the valve in many different working conditions. However, the correct and reasonable choice of valve material can obtain the most economical service life and the best performance of the valve.
In the classification of valve parts materials, the most general method is to divide the materials used in the housing: such as cast iron valves, the housing material is made of gray cast iron, malleable cast iron or ductile iron; Flash made of steel, alloy steel or stainless acid-resistant steel; titanium valve, valve made of titanium alloy for the housing; copper valve, valve made of copper alloy for the housing; aluminum valve, aluminum alloy for the housing Valves; plastic valves, valves made of plastic in the housing; ceramic valves, valves lined with ceramic in the housing, etc.
1, cast iron valve
Cast iron valves are widely used in various sectors of the national economy due to their low price, simple manufacturing process and good corrosion resistance. They are watercourses, construction equipment, gas equipment, ships, fire equipment, petrochemical equipment, ironmaking equipment, and food. Indispensable piping accessories such as processing equipment. The operating temperature range of cast iron valves is usually from ambient (room temperature) to below 225 ° C. However, because gray cast iron is a brittle material, the range of use of cast iron valves is limited.
In cast iron valves, due to changes in the internal microstructure of malleable cast iron and ductile cast iron, the structure of the malleable cast iron is near ferrite and the center is pearlite, which is roughly the same as that of mild steel. Ductile iron is added with elements and modified, and nodular graphite is obtained during the casting process. Therefore, its mechanical properties are much better than ordinary gray cast iron, and its working pressure can be higher.
Generally, the range of use of cast iron valves is as follows:
(1) When used for nominal pressure PN≤1.0MPa, working temperature is -10 ～ 200 ℃, working medium is water, seawater, steam, air, gas, oil, etc., generally the brand names are HT200, HT250, HT300, HT350 Gray cast iron valve.
(2) When used for nominal pressure PN≤2.5MPa, working temperature is -30 ～ 300 ℃, working medium is water, seawater, steam, air, gas, oil, etc., usually the brands KTH300-06, KTH330-08 KTH350-10 malleable cast iron valve.
(3) When used for nominal pressure PN≤4.0MPa, working temperature is -30 ～ 350 ℃, working medium is water, seawater, steam, air, gas, oil, etc., usually the brands QT400-15, QT450-10 , QT500-7 ductile iron valve.
Due to the different types of steel used, the applicable media for steel valves are also very different. Although the price of steel valves is relatively expensive, because steel is a plastic material and has a wide range of applications, it can be used in various media such as tungsten Saturated steam and hot steam, high and low temperature oils, liquefied gases, corrosive media, etc., are widely used.
Carbon steel, due to its excellent mechanical properties and comprehensive use performance, therefore, has a wider range of use, usually including cast iron valves and bronze valves (widely used below -180 ℃) working conditions. Generally, sturdy and reliable steel valves are used on important equipment, devices and pipelines. Steel valves must be used where the medium is flammable gas, liquid, toxic gas, liquid, flammable and explosive medium, compressed gas, liquefied gas, power plant pipelines, and other similar occasions.
Special carbon steel and low-nickel alloy steel can be used in the working temperature below zero, but can not be used in the deep cold area. Valves made from these materials may be suitable for media such as seawater, carbon dioxide, acetylene, propylene and ethylene.
Corrosion-resistant steel includes stainless steel, special stainless steel, "Monel" alloy, Hastelloy "B", Hastelloy "C", stainless acid-resistant steel, etc.
Stainless steel acid-resistant steel valves can be widely used in chemical and food industries. Such as the pipeline of acetic acid, nitric acid, sulfuric acid, alkali, western bleach, food, fruit juice, carbonic acid, tanning liquid and many other chemical products. Ultra-low-carbon austenitic stainless acid-resistant steel valves are usually used to transport liquid gases at low temperatures, such as natural gas, biogas, oxygen, and hydrogen. Special stainless steel valves have good corrosion resistance, and are usually used on pipelines and devices that transport sulfuric acid of various temperatures and concentrations. "Monel" alloy valves are mainly used in pipelines and devices for transporting alkali, salt solutions, food and many inorganic acids, especially sulfuric acid and hydrofluoric acid. In addition, these valves can also be used in steam and seawater pipelines. Nickel valve has strong corrosion resistance to alkali and salt solutions. It is usually used in product transportation and requires high purity working conditions. "Hasse" alloy valve is mainly used for pipelines and devices for transporting strong corrosive media such as ammonium chloride, zinc chloride, aluminum sulfate, ammonium sulfate, hydrochloric acid.