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Reason: Since pressure vessels are special equipment with explosion hazards, over the years, **the safety supervision authorities for boilers and pressure vessels have promulgated a series of regulations as well as corresponding product standards.** In view of the characteristics of pressure vessels, technical requirements for the materials used in such vessels have been specified. When selecting steel for pressure vessels, the following points should be taken into account. 1 When selecting materials for pressure vessels, it is necessary to consider the operating conditions of the vessel, such as temperature, pressure, and the properties of the medium ； The performance characteristics of the material, such as mechanical properties, physical properties, and chemical properties ； Machinability, such as the material’s weldability and hot/cold workability ； Economic feasibility, such as material cost, manufacturing expenses, and service life. 2 Materials for pressure vessels shall be selected in accordance with the materials listed in the **standard ‘Pressure Vessels’. The standard stipulates that the design pressure should not exceed 35 MPa. For cases exceeding this limit, a specific analysis and testing must be conducted; a decision can then be made after thorough research. 3 The maximum operating temperature for steel materials shall not exceed the upper limit temperature corresponding to the allowable stress of each steel grade. However, it should be noted that when carbon steel and carbon-manganese steel are used for extended periods at temperatures above 425°C, the tendency of the carbides in the steel to graphitize must be taken into account. When austenitic steel is used at temperatures above 525°C, its carbon content should not be less than 0.04%. For