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Material requirements: The main requirements for material selection in pressure vessels are as follows. 01 The quality and specifications of the materials used for pressure vessels shall comply with the requirements specified in TSG21—2016 \"Regulations on Safety Supervision of Fixed Pressure Vessels\". The material manufacturers shall provide the users with a quality certificate (in original form) in accordance with the relevant standards, and shall affix clear and durable stamp marks or other identifiers in prominent positions on the materials; such identifiers shall include at least the code of the material manufacturing standard, the material grade and specifications, the furnace (batch) number, a mark recognized by the safety supervision authority, the name of the material manufacturer, and a inspection seal mark. 02 When selecting materials for pressure vessels, in addition to mechanical properties and bending strength, compatibility with the medium must also be taken into account. The phosphorus content (as determined by melting analysis, the same applies hereafter) in the steel specifically intended for pressure vessels should not exceed 0.030%, while the sulfur content should not exceed 0.020%. When pressure vessels (excluding glass-lined pressure vessels) are manufactured using carbon steel boiling steel plates and carbon steel killed steel plates, they shall comply with the provisions of GB150.2—2011 \"Pressure Vessels – Part 2: Materials\". Carbon steel boiling steel plates and Q235A steel plates shall not be used to manufacture pressure vessels that are directly exposed to flame heating. 03 For carbon steel and low-alloy steel used in the main pressure-bearing elements of welded structural pressure vessels, the mass fraction of carbon shall not exceed 0.25%. 04 The mechanical properties, bending properties, and impact test requirements for materials used in steel pressure vessels (such as steel plates, forgings, steel pipes, studs, etc.) shall comply with the relevant provisions of **. 05 Carbon steel and low-alloy steel plates used for manufacturing pressure vessel shells shall comply with the requirements for ultrasonic testing of steel plates specified in 2.2.1.4 of the “Safety Technical Supervision Regulations for Stationary Pressure Vessels” under TSG21—2016. Ultrasonic testing shall be performed on each unit that meets one of the following conditions: a. Pressure vessels containing media with an extremely high or high degree of toxicity ； b. Pressure vessels filled with liquefied petroleum gas and containing more than 100 mg/L of hydrogen sulfide ； c. Pressure vessels with a maximum operating pressure of 10 MPa or greater ； d. Steel plates that require ultrasonic testing on a sheet-by-sheet basis as specified in GB151-2014 \"Heat Exchangers\", GB12337-2014 \"Steel Spherical Storage Tanks\" and other **national and industry standards. 06 Mobile pressure vessels. ①The ultrasonic testing of steel plates shall be carried out in accordance with the provisions of NB/T 47013.3-2015 \"Non-destructive testing of pressure equipment – Part 3: Ultrasonic testing\". ②In accordance with TSGR0005-2011 \"Safety Inspection Regulations for Mobile Pressure Vessels\", for the tanks of mobile pressure vessels, 2 steel plates shall be sampled from each batch to undergo Charpy (V-notch) low-temperature impact tests at a temperature of -20°C or as specified in the drawings; the sampling direction for the test specimens shall be horizontal. The low-temperature impact energy absorption index shall comply with relevant regulations. 07 Requirements for cast iron used in pressure vessels. ①It must be selected within the corresponding **standard range, and the material grade used for casting shall be specified in the product quality certificate. ②The design pressure and design temperature shall comply with the following requirements: a. The design pressure of gray cast iron pressure vessels shall not exceed 0.8 MPa, and the design temperature shall be 0–250℃ ； b. The design pressure of pressure vessels made of malleable cast iron and ductile iron shall not exceed 1.6 MPa, and the design temperature shall be between -10°C and 350°C. 08 The cast steel materials used for the pressure-bearing components of pressure vessels shall be selected in accordance with TSG21-2016, and the grade of the material used in casting shall be specified in the product quality certificate. Cast steel materials should not be used for the cylinders and heads of pressure vessels (except in cases where the pressure vessel manufacturer has prior experience in using such materials and it has been approved by the provincial or relevant safety supervision agency). 09 The requirements for non-ferrous metals used in pressure vessels (namely aluminum, titanium, copper, nickel, and their alloys) are as follows: ① Non-ferrous metals used in the manufacture of pressure vessels shall be selected in accordance with TSG21—2016. When there are special requirements for non-ferrous metals, they must be specified in the design drawings or corresponding technical specifications. ②The manufacturing unit must establish a strict material storage system and designate a specific area for storing them. ③The impact test requirements for materials used in pressure vessels made of non-ferrous metals shall comply with the provisions of the relevant standards. ④The grooves of welded joints on pressure vessels made of non-ferrous metals shall be machined by mechanical means; their surfaces must be free from defects such as cracks, layering, and slag inclusions. 10 According to the provisions of TSG21-2016, aluminum and aluminum alloys used for pressure-bearing components of pressure vessels must meet the following requirements: ① The design pressure shall not exceed 8 MPa, and the design temperature range is from -269 to 200°C. ②When the design temperature is greater than 65°C, aluminum alloys with a magnesium mass fraction of 3% or higher are generally not selected. 11 When copper and copper alloys are used for pressure-bearing components in pressure vessels, they should generally be in an annealed state. 12 Pressure vessels manufactured from titanium materials (referring to industrially pure titanium, titanium alloys, and their composite materials; the same applies hereafter) for use as pressure-bearing components shall meet the following requirements: a. Design temperature. Industrial pure titanium should not exceed 230°C, titanium alloys should not exceed 300°C, and titanium composite sheets should not exceed 350°C℃ ； b. Titanium materials used for manufacturing pressure vessel shells shall be used in the annealed state ； c. For forming heads of pressure vessels made of titanium materials, hot forming or cold forming followed by hot straightening shall be employed. For formed titanium-steel clad plate heads, ultrasonic testing shall be conducted ； d. Titanium pressure vessels generally do not require heat treatment; however, titanium vessels used in stress-corrosion environments or those manufactured from medium-thickness plates should undergo stress-relief annealing after welding or hot working ； After explosive bonding of titanium-steel clad plates, stress-relief annealing should be performed ； e. The welds of titanium pressure vessels shall be subject to penetrant testing. 13 When pressure vessel pressure-bearing components are manufactured from nickel materials (referring to nickel and nickel-based alloys as well as their composite materials, the same below), the following requirements shall be met: a. Design temperature. Pure nickel in the annealed state should not be exposed to temperatures above 650°C; nickel-copper alloys should not exceed 480°C; nickel-chromium-iron alloys should not go above 650°C; and nickel-iron-chromium alloys should not reach temperatures above 900°C℃ ； b. Nickel materials used for manufacturing the main pressure-bearing components of pressure vessels should be used in the annealed state, while pure nickel tubes for heat exchangers should be used in the stress-relieved annealed state ； c. When hot-forming the heads of nickel pressure vessels, the heating temperature must be strictly controlled ； Ultrasonic testing should be performed on the formed nickel-steel composite plate heads ； d. The heating temperature and furnace atmosphere for the thermal shaping of nickel materials must be strictly controlled to prevent sulfur embrittlement contamination ； e. Nickel-based pressure vessels generally do not require post-weld heat treatment; if such treatment is necessary, it should be specified in the drawings ； After explosive bonding of nickel-steel composite plates, stress-relief annealing should be performed ； f. The welds of nickel pressure vessels shall be inspected by magnetic particle or penetrant testing. 14 When pressure vessel components are made of foreign materials, the following requirements must be met: a. Materials that are permitted for use according to foreign pressure vessel standards and for which there are existing examples of use abroad should be selected; their scope of use shall comply with the relevant regulations and standards of the country where the material is produced, and a quality certificate for such material must be available ； b. Before being used for the first time by the manufacturing unit, welding procedure qualification and welder testing must be carried out, and the chemical composition and mechanical properties must be rechecked; only after meeting the requirements can the material be used for production ； c. The technical requirements generally shall not be lower than the technical specifications of corresponding domestic materials ； d. Materials that are used for the first time in the domestic market and for which the specified minimum value for tensile strength in the standards is 540 MPa or higher must go through the required approval procedures. 15 For pressure vessels, the main pressure-bearing components are made from newly developed materials (including imported materials for which there are no application examples domestically or internationally), or from materials not specified in standards such as GB150-2011 \"Pressure Vessels\". The manufacturers of such materials shall submit test and verification data sowie third-party inspection reports to the National Pressure Vessel Standardization Technical Committee for technical evaluation, and obtain a certification document issued by this committee granting permission for trial use (specifying the conditions under which the materials may be used), followed by going through the required approval procedures. 16 Welding materials used for manufacturing the pressure-bearing components of pressure vessels shall be manufactured, inspected, and selected in accordance with relevant standards. Welding materials must have a quality certificate and clear, durable markings. 17 The materials used for manufacturing pressure vessels are selected primarily based on the process conditions of the vessel (pressure, temperature, properties of the medium) and the method of vessel fabrication. The general requirements are good plasticity, good toughness, and an appropriate strength limit. For welded vessels, the material must have good weldability, while for vessels exposed to corrosive media, the material must possess strong corrosion resistance. The carbon content in Q235AF boiling steel is approximately 0.14%–0.22%. It possesses good plasticity; its tensile strength at room temperature is greater than 380 MPa, its yield strength is greater than 240 MPa, and its elongation is greater than 25%. However, due to incomplete deoxidization during the boiling process, iron oxide or bubbles are present in the steel, resulting in a porous structure and lower quality. In particular, self-crazing may occur after welding after a certain period of time, so it is generally not suitable for manufacturing welded pressure vessels.