A pressure vessel is a closed vessel that can withstand pressure. The pressure vessel has a wide range of uses, and it plays an important role in many sectors such as industry, civil and military industry, as well as in many fields of scientific research. 

Precautions for use of pressure vessels

The pressure

The pressure of a pressure vessel can come from two aspects. One is that the pressure is generated (increased) outside the vessel and the other is that the pressure is generated (increased) inside the vessel.

Maximum working pressure refers to the maximum pressure that may occur at the top of the container under normal operation.

Design pressure refers to the pressure used to determine the thickness of the vessel shell at the corresponding design temperature, that is, the design pressure of the vessel marked on the nameplate. The design pressure of the pressure vessel shall not be lower than the maximum working pressure; When the static pressure of the liquid column borne by each part of the container or the pressurized component reaches 5% of the design pressure, the sum of the design pressure and the static pressure of the liquid column should be taken for the design calculation of the part or component; The design pressure of a pressure vessel equipped with a safety valve shall not be lower than the opening pressure or bursting pressure of the safety valve. The design pressure of the vessel shall be determined in accordance with the corresponding provisions of GB 150.

The temperature

Metal temperature refers to the average temperature of the pressurized element of the vessel along the thickness of the section. In no case shall the surface temperature of the component metal exceed the allowable service temperature of the steel.

Design temperature refers to the maximum or minimum temperature that the shell wall or element metal may reach under the corresponding design pressure under normal operation of the vessel. When the temperature of the shell wall or component metal is lower than -20 ℃, the design temperature is determined according to the lowest temperature; In addition, the design temperature is selected according to the highest temperature. The design temperature value shall not be lower than the highest possible metal temperature for the component metal; For metal temperatures below 0 ° C, the design temperature shall not be higher than the lowest possible metal temperature for the component metal. The design temperature of the vessel (i.e. the design medium temperature marked on the vessel nameplate) refers to the design temperature of the shell.

The medium

There are many kinds of media involved in the production process, and there are many kinds of classification methods. According to the state of matter classification, there are gas, liquid, liquefied gas, elemental, and mixture; According to the classification of chemical characteristics, there are combustible, flammable, inert, and combustion-supporting four kinds; According to their degree of toxicity to human beings, they can be divided into four levels: extreme hazard (I), high hazard (II), moderate hazard (III) and mild hazard (IV).

Flammable medium: refers to the gas with a lower limit of explosion mixed with air is less than 10%, or the difference between the upper limit of explosion and the lower limit is greater than or equal to 20%, such as methylamine, ethane, ethylene, etc.

Toxic media: The division of degree of media toxicity in Pressure Vessel Safety Technical Supervision Regulations (hereinafter referred to as the Volume Regulation) is divided into four levels according to GB 5044 "Occupational Exposure to Toxicants Hazard Degree Classification". The maximum allowable concentrations are: extremely hazardous (grade I) & LT; 0.1mg /m3; High hazard (Class ⅱ) 0. 1 ~ & LT; 1.0 mg/m3; Moderate hazard (grade ⅲ) 1.0 ~ < 10 mg/m3; Mild hazard (grade 1V) ≥10 mg/m3.

When the medium in the pressure vessel is a mixed substance, the degree of toxicity of the medium or whether it belongs to a flammable medium should be determined by the process design department of the designing unit or the production technology department of the using unit according to the composition of the medium and the division principle of the degree of toxicity or flammable medium.

Corrosive medium, petrochemical medium to pressure vessel materials have corrosion resistance requirements. Sometimes because there are impurities in the medium, the corrosion is aggravated. The types and properties of corrosive media are not the same, and the process conditions are different, the corrosion of the medium is not the same. This requires the pressure vessel in the selection of materials, in addition to should meet the mechanical properties under the conditions of use, but also having enough corrosion resistance, if necessary, but also taking certain anti-corrosion measures.