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Mandatory requirements for medium-pressure vessels: Mandatory requirements for vessels in the medium-pressure range (1.6 MPa ≤ P < 10 MPa). 01 Design pressure limit for cast steel vessels: For carbon steel or low-alloy carbon-manganese steel, the design pressure shall not exceed 2.5 MPa； Low-alloy chromium-molybdenum steel, with a design pressure not exceeding 4.0 MPa ； High-alloy austenitic heat-resistant steel, with a design pressure not exceeding 4.0 MPa. 02 For Class III pressure vessels with a design pressure of 1.6 MPa or higher, all butt joints of shells of Classes A and B shall undergo non-destructive testing (RT/UT). 03 Type I fiber-reinforced plastic pressure vessels manufactured using the winding process, when no pole hole envelopment is applied, shall have a design pressure not exceeding 10 MPa. 04 For Class III pressure vessels with a design pressure of 1.6 MPa or greater, undergoing their first periodic inspection, the length required for detecting surface defects shall be not less than 20% of the length of the butt welds. 05 The accuracy of the pressure gauge used in the container must be no lower than grade 1.6. 06 Before installation and use, the level gauge for containers must undergo a hydraulic test at 1.5 times the nominal pressure of the gauge. 07 When the design pressure is ≥ 4.0 MPa, steel pipes specified in GB/T8163 such as grades 10, 20, and Q345D shall not be used. 08 When the design pressure is ≥1.6 MPa, Q235 series steel plates shall not be used for pressurized components.