The process conditions of chemical production process are very complex, with pressure ranging from vacuum to high pressure and even ultra-high pressure; The temperature ranges from deep cold to high temperature; The medium is corrosive, flammable, explosive, toxic, and even highly toxic.
In order to ensure the safe operation of chemical equipment, there are high requirements for the reliability of the selected chemical equipment materials in the planning. The commonly used materials for chemical equipment can be divided into two categories: metallic and non-metallic. Metal materials are commonly used during this process. There are many factors to consider when selecting materials.
The general requirements for materials are as follows:
1. Should have satisfactory strength and stiffness; Outstanding plasticity and durability.
2. It has a certain corrosion resistance function in the medium in which it is located.
3. Outstanding processing technology and function
4. Wide range of resources, sufficient supply, and reasonable economy.
Function of Materials
1. Mechanical function
Mechanical function refers to the characteristics that a material possesses during the process of being subjected to external forces and deformation. The mechanical functional goals of materials are experimentally measured.
① Strength
Strength refers to the ability of a material to resist damage under external forces.
The strength targets of materials at room temperature include yield limit and strength limit. The yield limit a is the stress value (MPa) at which a material undergoes plastic deformation under external forces. The strength limit a is the stress value (MPa) that a material can accept before cracking and damage occurs under external forces.
These two strength targets are the basis for determining the allowable stress of the material when operating at room temperature. The phenomenon of slow plastic deformation of metal materials during long-term operation under high temperature and stable load is called "high-temperature creep" of the material.
② Stiffness
Stiffness refers to the ability of a material to resist deformation under external forces.
③ Stability
Stability refers to the ability of a component to maintain its original equilibrium state under external forces. The stability parameters of the material are the elastic modulus E and Poisson's ratio u.
④ Plasticity
Plasticity refers to the plastic deformation that a material can experience before being damaged by external forces. Elongation and cross-sectional shortening are the plastic goals of materials.
⑤ Endurance
Cracking toughness and impact resistance are both the durability goals of materials. Cracking toughness K refers to the stress intensity factor that a material should have when it does not crack, and is the inductive goal of strength and plasticity
⑥ Hardness
Hardness is a functional parameter that measures the softness and hardness of a metal material, indicating its ability to resist elastic deformation, plastic deformation, and fracture within a certain volume of the outer surface. There are different hardness targets due to different experimental methods.
2. Physical functions
The physical functions of materials include density, melting point, thermal expansion, thermal conductivity, conductivity, magnetism, elasticity, etc. These functions are necessary to meet the requirements of planning parameters for reciprocating motion machinery, rolling machinery, and heat exchange equipment.
3. Chemical function
The chemical function of metal materials here primarily refers to the chemical stability of the material in the medium in which it is located. The materials used for making equipment should not only not pollute the medium but also have satisfactory corrosion resistance during operation.
4. Process function
The process function of metals refers to the functions that materials can be processed, such as castability, malleability, weldability, and cutting ability | 
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