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For pressure vessels, the proper selection and application of materials are extremely important. When selecting materials, it is necessary to take into account their mechanical properties, chemical properties, physical properties, and processability. Additionally, factors related to the operating environment of the pressure vessel must be considered, such as design pressure, design temperature, characteristics of the medium, the weldability of the material, inspection and testing requirements, heat treatment needs, as well as economic feasibility. The general principles for selecting steel plates for pressure vessels are as follows: (1) In applications where stiffness and structural design are of primary importance, ordinary carbon steel should be preferred whenever possible. In applications where strength-based design is prioritized, it is advisable to select steel grades such as Q235B/Q245R/Q345R based on usage constraints such as pressure, temperature, and the type of medium. (2) When the steel plate thickness is less than 8 mm, carbon steel is preferred over low-alloy steel. (3) When the thickness of stainless steel is greater than 12 mm, structural forms such as stainless steel lining, composite construction, or surfacing welding are advisable. (4) Stainless steel is not suitable as a heat-resistant steel for design temperatures of 500°C or less. (5) Stainless steel can be used in heat-resistant steels that are exposed to highly corrosive media, to prevent iron ion contamination, or in applications with design temperatures above 500°C. It can also be used in low-temperature steels for applications with design temperatures ranging from -100°C to -196°C. (6) Chromium-molybdenum low-alloy steel can be used to manufacture heat-resistant steels for design temperatures of 550°C or less, or hydrogen-resistant steels for temperatures above 200°C. (7) When carbon steel and carbon-manganese steel are used for extended periods at temperatures above 425°C, the tendency of the carbide phases in the steel to graphitize should be taken into account. (8) When austenitic steel is used at temperatures above 525°C, its carbon content should be not less than 0.04%. In short, in principle, selection should be made in the following order; prefer the former whenever possible over the latter. (1) Thin plates – clad plates – thick plates; (2) Carbon steel – low-alloy steel – austenitic stainless steel – duplex stainless steel – titanium and titanium alloys – nickel alloys – zirconium materials; (3) Cold-rolled condition – hot-rolled condition – normalized condition – normalized and tempered condition – quenched and tempered condition