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Large studs: Some requirements for large studs are as follows: 01 When the nominal diameter of the bolt is greater than 48 mm, fine-thread threads should be used. 02 For studs and nuts with a nominal diameter greater than M36, the following requirements apply: (1) A hardness test must be conducted on the heat-treated nut blanks ； (2) The studs shall undergo surface inspection and must meet Grade I standards. Welding of dissimilar steels: Mandatory requirements for containers welded with dissimilar steels are as follows: 01 The surface of the welds between dissimilar steels must be inspected using magnetic particle or penetrant testing. 02 The impact test requirements, as well as the tensile and bending property requirements, for the weld metal of low-temperature vessels shall be in accordance with the lower requirements of the base materials on both sides. 03 For weld joints between dissimilar steels (i.e., materials of different grades), PWHT is determined based on the more stringent heat treatment requirements. 04 Welded joints of dissimilar steels (i.e., those for which the welding processes are not compatible with each other; according to NB/T 47014, higher categories can cover lower categories, and higher groups can cover lower groups) shall have their surfaces inspected using magnetic particle or penetrant testing. 05 When welding steels of different strengths together, the preheating temperature appropriate for the steel with the higher strength should be used.