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Mandatory requirements for cryogenic containers: The mandatory requirements for cryogenic containers (≤-20°C) are as follows: 01 Low-temperature and low-stress conditions are not suitable for materials with Rm≥540 MPa, nor for bolt materials. 02 The supports or legs of the container must not be welded directly to the shell; shims must be used. 03 For welds of categories A, B, C, and D in low-temperature vessels, a fully penetrative weld structure shall be employed, while for category E welds, continuous welding shall be used. 04 Welding electrodes for low-temperature vessels shall be retested in batches for the moisture content in the flux or the diffused hydrogen content in the deposited metal. 05 Hard-print markings shall not be used on the pressure-bearing components of low-temperature vessels. 06 There shall be no undercut on the surface of the container welds. 07 If any welding repairs are carried out after post-weld heat treatment, the repaired area should be heat-treated again. 08 When there are longitudinal welded joints of Type A (excluding Type A joints where the sphere is connected to a cylinder), welding test pieces for the products shall be prepared one by one. 09 The impact test shall include the weld metal and heat-affected zone. 10 For low-temperature vessels with a design temperature of < -40°C or a weld joint thickness of > 25 mm, 100% non-destructive testing (RT/UT) shall be conducted on Class A and Class B weld joints. On low-temperature vessels with 100% non-destructive testing of Class A and B welds, the surfaces of welding joints of Classes A, B, C, D, and E, the surfaces of areas where defects have been ground out or rewelded, and the surfaces of cut marks resulting from the removal of clamps and tie rods, shall be subjected to magnetic particle or penetrant testing. 12 The nameplate cannot be directly anchored to the housing. 13 The steel plates for low-temperature spherical tanks shall be in the normalized or quenched and tempered condition. 14 For all cryogenic spherical tanks, magnetic particle testing or penetrant testing shall be conducted on the surfaces of all weld joints (A, B, C, D, E), as well as on the welds left by welding fixtures and on areas where defects have been ground and repaired.