[introduction] materials commonly used in chemical equipment (material): the process conditions of the chemical production process is very complicated, pressure from vacuum to high pressure and ultra high pressure; temperature from Cryogenic to high temperature; the medium is corrosive, flammable and explosive, poisonous or toxic. In order to ensure the safe operation of chemical equipment, the design of the chemical equipment in the selection of the reliability of the material has a very high demand. Chemical equipment commonly used materials can be divided into two categories of metal and nonmetal. Which is the most widely used metal materials. There are many factors to consider when selecting a material.

The general requirements for the material are as follows:
1, should have enough strength, stiffness, good plasticity, toughness.
2, in the medium with a certain corrosion resistance.
3, good processing technology.
4, a wide range of resources, adequate supply, economic and reasonable.
First, the performance of materials

(a) mechanical properties
Mechanical properties are the properties of the material in the process of external force and deformation. The mechanical property of the material is measured by the test.
1, strength
Strength is the ability of the material to resist damage under the action of external forces. The strength index of the material at room temperature has yield limit and ultimate strength. The yield limit of a is the minimum stress value (MPa) of the material under the action of external force. A is the maximum stress value (MPa) which can be subjected to the material under the action of external force.
These two strength indexes are the basis for determining the allowable stress of materials at room temperature. Under high temperature and constant load, the metal materials can produce slow plastic deformation, called “ high temperature creep ”.
2, stiffness
Stiffness refers to the ability of the material to resist deformation under the action of external force.
3, stability
Stability is the ability of the component to maintain its original equilibrium state under the action of external force. The stability parameter of the material is elastic modulus E and Poisson's ratio U.
4, plastic
Plasticity is the plastic deformation ability that the material can withstand before being destroyed by the external force. The elongation rate and section shrinkage are the plastic index of the material.
5, toughness
Fracture toughness and impact toughness are all toughness indexes of the material. Fracture toughness K is a composite index of strength and plasticity, which is a composite index of strength and plasticity.
6, hardness
Hardness is a measure of the degree of hardness of metal materials, it is a kind of performance parameters, which indicates that the local volume of the metal surface to resist elastic deformation, plastic deformation and breaking capacity. Because of different test methods, there are different hardness indicators.
(two) physical properties
The physical properties of materials are density, melting point, thermal expansion, thermal conductivity, electrical conductivity, magnetism, elasticity and so on. These properties must meet the requirements of the design parameters of reciprocating machinery, rotating machinery and heat exchange equipment.
(three) chemical properties
The chemical properties of the metal materials are mainly the chemical stability of the materials in the medium. The material of the manufacturing equipment should not only be contaminated in the work, but also has enough corrosion resistance.
(four) process performance
The process performance of the metal is the performance of the material can be processed, such as casting, forging, welding, machining, heat treatment and cold bending properties.

Two, the classification of materials

Engineering materials, including metal materials, organic polymer materials (resin), inorganic non-metallic materials (including ceramic materials), including the three series of the full range of materials. Metal materials are the main materials for the manufacture of chemical equipment.
Three, the classification of metal materials

Metal materials are divided into two categories: ferrous metals and non-ferrous metals.
Black metal is the general name of iron and steel, ferrous metal is divided into pig iron and steel.
Pig iron can be divided into steelmaking pig iron, cast iron and alloy pig iron.
The steel can be divided into carbon steel and alloy steel.
Non ferrous metals, including copper, aluminum, lead, nickel, titanium and its alloys. Steel and iron are alloys of iron and carbon.
Iron carbon alloy by about 95% of the Fe elements, 0.05% ~ 4% of the C elements and ore in the original and smelting process into about 1% of the impurities. These impurities are mainly Mn, Si, S, P, O, N, H and other elements.
Steel and iron are classified according to their chemical composition:
Carbon containing 2% to 0.02% of the steel.
Carbon containing more than 2% of the cast iron (C > 4.3% no use value).
The carbon content is less than 0.02% of the industrial pure iron (rarely used).
Carbon content has a decisive influence on the mechanical properties of steel.
In general, the increase in carbon content will increase the strength and hardness of steel, plastic and toughness decreased.
Industry is the largest application of steel. A lot of classification methods of steel. According to the classification of chemical composition, according to the quality classification, according to the smelting method classification, according to the metallographic organization classification and the classification method according to the use classification.
According to the chemical composition can be divided into: carbon steel and alloy steel.
According to the quality can be divided into:
Ordinary steel (S≤ 0.050%, P≤ 0.050%), high quality steel (S≤ 0.040%, P≤ 0.040%) and high quality steel (S≤ 0.02% ~ 0.03%, P≤ 0.035% ~ 0.03%).
According to the classification of smelting method, according to the different smelting furnace is divided into: steel, steel, electric steel;
According to the degree of deoxidation and pouring system is further divided into: Steel (deoxidation completely, good quality, high price), boiling steel (symbol F, DNA incomplete, poor quality, low price), SEMIKILLED steel (the symbol B, performance characteristics between the former two).
According to the microstructure can be divided into categories: ferritic steel, austenitic steel, you can also press the heat treatment method for further classification, steel, normalizing annealing conditions such as the state of the steel, no phase or part of phase change of steel.
According to the use can be divided into: Construction and engineering with steel, structural steel, tool steel, special steel, professional steel. Such as bridge steel (Q)Boiler steel (g), container steel (R), welding rod steel (H), etc..
China's steel “ &rdquo classification; national standard (GB / T133049P) is according to the international standard (ISO4948 / 1, ISO4948 / 2) set.
The first part, according to the classification of chemical;
The second part, according to the main quality level, the main performance and the use of feature classification.
Four, chemical commonly used non-metallic materials
Materials in accordance with their chemical characteristics, generally divided into two categories of inorganic materials and organic materials.
1, inorganic non-metallic materials
The traditional inorganic non-metallic materials mainly refers to ceramic, glass, cement and refractory materials for chemical class four, the four kinds of materials are composed of silicate, is also called silicate material, because the ceramic material has a long history, the most widely used, is often referred to as ceramic materials.
Since 1940s, with the development of science and technology, the traditional silicate materials technology has gradually developed into a new type of inorganic non-metallic materials science and engineering.
In this field, the research and development work is active and is in the front of the whole material science and engineering development, especially the research of advanced ceramics, amorphous materials, artificial crystal and inorganic coating technology.
Inorganic non-metallic materials are generally corrosion resistant, brittle, not resistant to temperature changes, can not be machined.
(1) chemical ceramics

The ceramic material has good chemical inertness, high temperature resistant performance, creep resistance, abrasion resistance, and the machine, electricity, sound, light, heat, magnetism, and elastic properties and the coupling between them more attention.
The generalized ceramic material contains the traditional ceramics, inorganic coating materials (enamel), amorphous materials (glass) and other ceramic materials except in hydrofluoric acid and alkali corrosion resistance both at home and abroad, general.
In the chemical industry, mainly used in the chlorine and hydrochloric acid industry. Ceramic tile, board and other materials can be used for equipment lining; ceramic can be used in acid and alkali corrosion, high temperature resistance, wear resistance and heat insulation (such as zirconia) coating materials to achieve the equipment efficiency or the purpose of life.
(2) chemical enamel

The enamel enamel glaze on the metal substrate, by high temperature sintering. Application of more acid resistant enamel (with steel or cast iron base material, also known as glass lining) and microcrystalline enamel (steel, stainless steel or alloy plate as substrate), far infrared radiation and high temperature enamel enamel (with stainless steel or alloy plate as substrate).
Enamel has good corrosion resistance, mechanical properties and electrical insulation properties. Can be used for enamel equipment or lining. The enamel has better physical properties, corrosion resistance of various chemical mediators, suitable for the production of the reaction tank, the polymerization kettle, vaporize, condenser, fractionating tower, storage tank, pump, valve, stirring of semi Acid Exchanger and pipeline
(3) diabase
Diabase after melting can cast plate, brick. Mainly used as equipment lining.
(4) glass

Chemical commonly used in chemical glass mainly boron glass, with heat resistance, high aluminum glass, with heat, corrosion resistance. Can be used to do pipe, pipe fittings, diaphragm valve, mirror, liquid level meter, etc..
(5) impermeable graphite
Graphite materials include two kinds of natural graphite and artificial graphite. Natural graphite mineral impurities content is big, not easy to select, can be used as a surface coating and colloidal lubricants, etc..
Artificial graphite is specially processed (such as organic material for carbonization and graphitization treatment) made of impermeable graphite with artificial graphite products as matrix impregnated resin matrix and pore filling, or with graphite powder and resin as binder, pressing or casting, also known as plastic graphite.
Impermeable graphite has the advantages of excellent corrosion resistance, good thermal conductivity, low coefficient of linear expansion, heat shock resistance, good processing performance and other characteristics. Commonly used in chemical equipment, such as block, tube and radial type graphite heat exchanger, graphite falling film absorber, concentrated sulfuric acid diluted with graphite, graphite hydrochloric acid synthesis furnace and corrosion resistant pipes and pipe fittings and bed plate, graphite safety sheet etc..
The chemical properties of the impermeable graphite are different with the properties of the impregnated resin. Phenolic impregnated graphite except strong oxidizing medium, strong alkali, resistant to various organic acid, inorganic acid, salt solution and various organic solvents, corrosion and leaching of furan resin and strong acid alkali resistant to oxidation, corrosion of PTFE impregnated graphite can resist various medium.
2, organic polymer materials
The organic polymer material has good processing property, corrosion resistance and low density, but it is generally not resistant to high temperature, and is not resistant to oxidation.
(1) engineering plastics
Plastic has a certain strength, easy molding, good welding performance; however, small thermal conductivity, coefficient of linear expansion of large (about 10 times that of steel), low impact toughness, poor heat resistance; many plastic low friction coefficient, good wear resistance and self lubrication.
In general, plastic and acid, alkali, salt, oil and water, and many other substances do not occur chemical reaction, but some of the plastic will be eroded.
According to the mechanical properties of different hard and tough plastic, such as polycarbonate, polyamide, polysulfone; hard and strong plastic, such as formaldehyde, epoxy reinforced plastics; hard brittle plastics, such as polystyrene, phenolic plastics, organic glass; soft and tough plastic, such as polyethylene, polyvinyl chloride etc..
Hard PVC plastic can be used for low pressure pipeline and equipment (often); polyethylene plastic has excellent insulation, waterproof and chemical stability, can be used as pipes, pipe fittings, valves, pumps and other materials, or as a lining, anti-corrosion coating; acid phenolic plastic PTFE plastic can be used as corrosion resistance, high temperature resistant sealing element of glass steel high strength, corrosion resistance, good processing performance.
(2) rubber

Rubber has two major types of natural and synthetic. Their common characteristic is the high elasticity, the permanent deformation is very small, has the good energy storage property and so on.
Rubber in the chemical industry, mainly used for dynamic and static seal. Such as all kinds of seals, bushings, gaskets, sealing, pipes and containers for shaft flange. Also can be used with other materials (metal, fiber) composite, used as a transmission hose, conveyor belt, such as the triangle belt.
(3) paint
Coatings include a variety of anti-corrosion paint, plastic paint (polyethylene, polyvinyl chloride), etc.Anticorrosive coating for equipment.
Five, chemical equipment material selection principle
1, follow the standard:
GB150-1998 "steel pressure vessel" "pressure vessel safety technology supervision regulation"
HGJ15-89 "steel chemical container material selection rules"
2. When the pressure vessel is made of ordinary low carbon steel, Q235B and Q235C are commonly used.
3, consider the economy
4, other guidelines:
A) for carbon steel, often low pressure vessel or wall thickness small pressure vessels in corrosive medium is not strong;
B low alloy steel, medium, high pressure vessel for medium corrosion resistance;
C) stainless steel for medium corrosive occasions;
D) heat resistant steel for high temperature applications;
E austenitic stainless steel can not be used for the occasion of intergranular corrosion;
5, the standard parts of the material selection in line with national standards or industry standards
6, the use of steel temperature to meet the requirements
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