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Austenite-ferrite duplex steel: Mandatory requirements for austenite-ferrite duplex steel vessels are as follows: 01 The steel plates used for the pressure-bearing components of pressure vessels must be produced using an off-oven refining process. 02 The surface of its welded joints needs to be inspected using magnetic particle (MT) or penetrant testing (PT). 03 Ferrite-austenite duplex steel plates for stressed components, with a minimum operating temperature of -20°C. 04 High-alloy steel forgings shall all be forged from steel that has undergone off-furnace refining. 05 For cylindrical, annular, and bowl-shaped forgings used as container shells and heads, grade III or grade IV should be selected. The minimum operating temperature for the steel forgings 06 S21953, S22253, and S22053 is -20°C. 07 The blanks for studs of various steel grades shall undergo tensile testing, and the testing requirements and results shall comply with the provisions of GB/T 1220. 08 There shall be no undercuts on the surface of the container welds. 09 Welded joints are generally not subjected to post-weld heat treatment. For 10 austenitic-ferritic stainless steels and their associated forgings, where the thickness of the welded joints is greater than 16 mm, Type A and Type B welded joints must undergo 100% non-destructive testing (RT/UT), while the surfaces of Type C, Type D, and Type E welded joints shall be inspected using magnetic particle or penetrant testing. 11 When the steel thickness is >20 mm, the surfaces of its butt and fillet joints shall be subjected to magnetic particle or penetrant testing.