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Mandatory requirements for low-temperature vessels: The mandatory requirements for low-temperature vessels (≤ -20°C) are as follows: 01 For vessels designed for temperatures below -40°C, the main pressure-bearing components shall be made of low-alloy steel that is not covered by the harmonized standards in these regulations; the material manufacturer must undergo a technical evaluation of the new material in accordance with the provisions of 1.9 before such material can be used. 02 When a material manufacturer manufactures for the first time low-alloy steel intended for pressure vessels with a design temperature below -40°C, it shall undergo a new material technology review in accordance with the provisions of 1.9. 03 For low-temperature steel plates and low-temperature steel forgings used in stressed components, a secondary refining process should be employed. 04 Carbon steels and low-alloy steels with a minimum standard tensile strength of 540 MPa or less, P≤0.025%, S≤0.012%. 05 Carbon steels and low-alloy steels with a minimum standard tensile strength of greater than 540 MPa, P≤0.020%, S≤0.010%. 06 The weld joints between the nozzles (flanges) of pressure vessels and the vessel shell, as well as the weld joints of jacketed pressure vessels, shall adopt a fully penetrative weld structure. 07 For low-temperature vessels made of carbon steel and low-alloy steel, product welding specimens shall be prepared. 08 For low-temperature vessels made of carbon steel and low-alloy steel, the proportion of local non-destructive testing shall be greater than or equal to 50%.